Inside Jokes



They love comic books, costumes, video games, and sci-fi in all forms of media, but what are the other recurring themes, jokes, and life experiences that make up Sheldon, Leonard, Howard, Raj, Penny, Amy, Bernadette, Stuart, and their Big Bang Theory characters we’ve been following for nine seasons? Just as each of those characters can be largely defined by his or her eccentricities (we could write a book on Sheldon alone), some of those quirks also point to how much each of them has evolved throughout the seasons (even if some of them still have a significant way to go). Here’s our rundown of all the Theory-isms that continue to keep the CBS sitcom churning after all these years.

Amy’s Crush on Penny  As the amount of affection she was getting from now-ex-boyfriend Sheldon increased, Amy’s crush on Penny cooled, but during the early seasons of the ladies’ friendship, Amy Farrah Fowler could not be less than subtle about her physical interest in Penny: She presented Penny with a painted portrait of the two of them, which Amy said had originally been a nude portrait; she drunkenly kissed Penny in season four’s “The Agreement Dissection,” and sang lyrics from Katy Perry’s “I Kissed a Girl”; and after Penny tried to explain Schrödinger’s Cat with a real-life example, Amy told her, “Homespun stories, knowledge of physics, and a bosom that defies it. You’re the whole package, aren’t you?” 

Anti-Christmas  Sheldon Cooper was initially a Grinch, hating on all things Christmas because his beloved Pop Pop died when he was 5, and Sheldon’s Christmas wish — to bring Pop Pop back — was denied. Through the seasons he’s made some happy holiday memories, though, like when Penny gave him Leonard Nimoy’s used napkin from the Cheesecake Factory in season two’s “The Bath Item Gift Hypothesis,” and when he and then-girlfriend Amy gave each other sweet gifts — homemade cookies from his grandma’s recipe for him, a personalized photo frame with a pic of Sheldon with Santa for her — in season eight’s “The Clean Room Infiltration.”

'''Bazinga! ''' Sheldon’s catchphrase, which he uses to indicate that he’s just made a joke. As his sense of humor, recognition of, and ability to use sarcasm has improved, his use of “Bazinga!” has decreased, with his most classic “Bazinga!” scene coming in season three’s “The Einstein Approximation,” where he repeatedly said the phrase while trying to evade Leonard in a giant ball pit.

Bernadette’s Mean  She’s a petite woman with a cartoonishly high-pitched voice and a sweet demeanor. But don’t let that fool you … Howard’s wife has a passive-aggressive tendency that, when paired with a set of lungs that can turn her squeaky voice into one that rivals that of Howard’s mother, can be truly frightening. Even her boss at the pharmaceutical company where Penny now also works is intimidated by Bernadette; Penny gets the job, in part, because she tells Dan she’s afraid of Bernadette finding out she did badly in the interview, which prompts Dan to admit he’s afraid of Bernadette, too, which is why he agreed to the interview in the first place.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Broken Elevator <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> The elevator in the apartment building where Sheldon, Leonard, and Penny live (2311 North Los Robles Avenue) has been out of order since before the series began. The culprit: Leonard Hofstadter, who had been working on a classified rocket-fuel project for the government. When he made a miscalculation of a batch of the fuel he had inside the apartment, Leonard tried to run the concoction outside via the elevator. Sheldon, realizing his roommate’s error, pulled Leonard out of the elevator and closed the door seconds before the lift exploded. Not only did Sheldon not narc on Leonard to the authorities or the landlord, he also helped him avoid prison, because Leonard’s girlfriend, Joyce Kim, was actually a North Korean spy who was sleeping with Leonard to get the scoop on the rocket fuel … until Sheldon kicked her out of their apartment. Leonard shared the story with Penny — in season three’s “The Staircase Implementation” — as the explanation for why he continues to live with Sheldon despite the fact he was warned by Sheldon’s old roommate (played by a pre–The Walking Dead Steven Yeun) to “Run away, dude … run fast, run far” before he moved in. As for repairing the elevator, the idea is mentioned occasionally, but producers have said it’s unlikely because the stairs provide a great opportunity for walk-and-talk scenes.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Cinnamon <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> She’s Raj’s Yorkshire terrier, given to him by Howard and Bernadette to help ease his loneliness. Raj is in the habit of spoiling his “special lady,” taking her for walks in a pink baby stroller, cooking her dinners of veal and scampi, and even sharing his toothbrush with her. His friends are notoriously not as attentive to the pooch; Bernadette and Howard lost her at the park, and Penny and Leonard didn’t notice she ate a box of Valentine’s Day chocolates while they were having sex. 

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Closure <span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111"> One of Sheldon’s many (many, many) quirks is his inability to proceed without closure. His face twitches if someone interrupts him, he has to complete his trademark knock even if the door is answered, and he calls the Syfy network when they cancel his favorite show, Alphas, without wrapping up a season-finale cliff-hanger. Amy spends an evening trying to help him break this OCD habit without getting closure herself.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Daddy Issues <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> Everyone’s got 'em. Penny wishes she were a boy. Sheldon’s father died when Sheldon was a teen. Leonard’s anthropologist father only spent time with Leonard when it involved research on the 2,000-year-old skeleton of an Etruscan boy. Amy’s father has never been mentioned. Raj’s doctor father still issues Raj an allowance. Bernadette’s dad is an Über-conservative retired cop who got drunk with Sheldon on Thanksgiving, and Mr. Wolowitz abandoned Howard and his mom when Howard was just 11.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Driver’s License <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Much to the annoyance of his friends, Sheldon must be chauffeured everywhere because he refuses to procure a driver’s license. The gang staged a license intervention in “The Euclid Alternative,” forcing him to try to learn how to drive on a simulation machine. But he never went further than getting a learner’s permit (which he only obtained because he annoyed the DMV clerk, played by a pre–Oscar win Octavia Spencer.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Emily Sweeney <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> Raj’s dermatologist girlfriend, who has an affinity for the dark side, including graveyard picnics and becoming a dermatologist because she likes to cut people, and her job makes it legally possible to do so. Raj acknowledges they’re very different people, but, as Howard points out, he’s unlikely to break up with a woman who’s having sex with him. Still, Sheldon predicts the gang will one day gather when “Koothrappali’s weird girlfriend admits where she buries his body,” so there may be a breakup on the horizon. Not to be confused with season five’s Emily, a deaf woman for whom Raj’s selective mutism was not an issue since she couldn’t hear him, but whose relationship with Raj was doomed because she was only using him for his money.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">The Enemies List <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Started when he was 9, Sheldon’s list of mortal enemies contains dozens of names, including Star Trek alum Brent Spiner, co-worker Barry Kripke, co-worker and Leonard’s ex-girlfriend Leslie Winkle, and, at one point, Penny. Another Trek alum, Wil Wheaton, has been on the list at various points, too, throughout his complicated relationship with Sheldon (see Wil Wheaton).

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Feelings <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> Sheldon has them, and doesn’t care for them. Just recently he wanted to go back to living old-school, where he didn’t get emotional about most other people, and certainly didn’t understand the emotions of other people. But nine seasons in, he’s got a whole group of friends he cares about, and, currently, an ex-girlfriend he’s pining for, so he has begrudgingly accepted that feelings are a part of his life now. As he admitted to Amy in season eight’s “The Prom Equivalency,” “I love you … there's no denying I have feelings for you that can't be explained in any other way. I briefly considered I had a brain parasite, but that seems even more far-fetched. The only conclusion was love.”

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">“Fun With Flags” <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> The full title is “Sheldon Cooper Presents: Fun With Flags,” and it is a podcast series in which Sheldon, with Amy’s help, teaches viewers all about vexillology, the study of flags. How much fun can one actually have with flags? A surprising amount, thanks to podcast guest stars like Wil Wheaton and LeVar Burton, and Amy’s willingness to dress up like a pretzel and a kangaroo to celebrate the flags of Bavaria and Australia, respectively. The most recent installment of “Fun With Flags” was decidedly less fun, as, post–breakup with Amy, Sheldon devoted the episode to the flags of countries he asserted had been torn asunder by women. The podcast is not Sheldon’s only nod to flags; there is an official flag of apartment 4A, the home he shares with Leonard. It’s a blue flag with a gold lion on it, and it can be seen, along with the U.S. flag, in every episode of “Fun With Flags,” as well as in magnet form on the apartment refrigerator. In times of distress, the flag is to be turned upside down. 

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Gift-Giving <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> Sheldon does not enjoy being the recipient of gifts because it creates a social contract in which the recipient is indebted to the giver until the recipient reciprocates with a gift. Or until one of the individuals dies.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Haemophobia <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> A phobia of blood, including one’s own. Like when Sheldon faints at the sight of his own bloody finger cut, then faints again when he shows the wound to Penny, in season five’s “The Vacation Solution.”

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Hot Beverage <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> According to Sheldon, social convention dictates you offer someone a hot beverage if he or she is upset.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Hot Cocoa <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> One of Sheldon’s favorite beverages, though he only drinks it during months that have an r in them. Why? “What’s life without whimsy?” he explains to Howard.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Howard’s Belt Buckles <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Howard’s got an impressive collection of belt buckles as part of his trademark wardrobe, which almost always also consists of a dickie and tight pants. Among the most memorable belt buckles in his lineup: Superman, Batman, a Nintendo controller, an alien, a robot, a chimpanzee, a sandwich, the Flash, Pac-Man, and one paying homage to his scooter. In season five’s “The Hawking Excitation,” Sheldon is tasked with polishing Howard’s bucket of buckles in exchange for Howard introducing him to Stephen Hawking. And Howard warns: Those water spots on the buckles? Not water. He stands too close to the urinal, so the buckles get “splashback.”

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Howie <span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111"> Bernadette’s nickname for her hubs, who frequently calls her Bernie.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal">'''<span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">“I’m Not Crazy. My Mother Had Me Tested.” '''<span style="font-size:7.5pt;font-family:"Georgia","serif";mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:"TimesNewRoman";color:#111111"> Sheldon’s oft-repeated response when he is often told that he’s crazy. His mother verified she did have him tested, and the doctor said he’s fine. But she also says she regrets not following up on that test with a visit to a specialist.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">The Knock <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> [Knock, knock, knock] “Penny.” [Knock, knock, knock] “Penny.” [Knock, knock, knock] “Penny.”

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">[Knock, knock, knock] “Amy.” [Knock, knock, knock] “Amy.” [Knock, knock, knock] “Amy.”

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">One of the most popular of Sheldon’s OCD tendencies, it’s become a T-shirt.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Kripke’s Rhotacism <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> The guys’ contentious Caltech colleague, Kripke, pronounces the lettersr and l as w, as when he threatens Sheldon, Leonard, Raj, and Howard that his “Kwipke Kwippwuh” — Kripke Krippler — will defeat their entry in a robot battle.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Laundry Night <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> For Sheldon it’s Saturdays at 8:15 p.m., in the basement laundry room of 2311 North Los Robles Avenue. Any deviation from this, or any part of his meticulously planned schedule, causes him great stress.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Meemaw <span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111"> Sheldon’s maternal grandma, widow of Pop Pop, Sheldon’s most beloved living relative, and the only person allowed to call him “Moonpie.” Meemaw has not yet appeared on the series, but a consensus among viewers is that Betty White should play her if she does.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Mommy Issues <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> Howard’s mother — the never-seen, often (and loudly) heard Debbie Wolowitz — died in season eight; Sheldon’s mother, Mary, is a Bible-quoting, no-nonsense Texan who never allows him to get too big for his britches when she’s around; and Leonard’s mother, Dr. Beverly, is a psychiatrist and neuroscientist who’s more impressed with Sheldon than she is with her own son, and who was so stingy with her affection that as a child, Leonard constructed a hugging machine (which his father would borrow). Amy’s mom is a strict and controlling woman who refused to let her watch Grease because she thought it would encourage Amy to join a gang, while Penny’s mom has never been seen or heard on the show, and Bernadette’s mom smoked while she was pregnant (leading, allegedly, to Bernadette’s four-foot-eleven frame), and pre-Howard, would lay out Bernadette’s daily outfits for her, even though they didn’t live in the same house.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Movie Theaters <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Sheldon won’t go to one alone, as there exists the possibility that he’ll choke on his popcorn and no one will be there to perform the Heimlich maneuver on him.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Penny No-Name <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> Until her season-nine-premiere marriage to Leonard, Penny had no last name. And as showrunner Steve Molaro told Vulture, there are no plans to reveal a surname for her, so Penny Hofstadter it is.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Penny’s Acting Career <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> She moved from Nebraska to California to pursue an acting career, but the highlights of Penny’s résumé include appearing topless in a low-budget movie called Serial Ape-ist; a hemorrhoid-cream commercial; a small part on NCIS that was cut before it aired (prompting an offer by her dad, Wyatt, to kick Mark Harmon’s ass); a bigger role in Serial Ape-ist 2: Monkey See, Monkey Kill; and several years as a waitress at the Cheesecake Factory. In the season-eight premiere, “The Locomotion Interruption,” she put her acting career on hold to take a well-paying job as a pharmaceutical sales rep at the company where Bernadette works.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Penny’s Dad Wanted a Boy <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> That’s why he called her Slugger and insisted on playing catch with her until she got her first training bra. And he still sends her gifts like a catcher’s mitt and baseball for Christmas. Leonard’s mother, while analyzing Penny during a walk up the stairs to Leonard’s apartment, suggests Penny became an actress because she seeks the approval she never really got from her father, and tells Leonard, “If you want to have intercourse with that girl, find out what kind of cologne her father wore.”

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Professor Proton <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Comedy and TV legend Bob Newhart won his first-ever Emmy (really) for playing Professor Proton, the host of a science-themed kids TV show beloved by Sheldon and Leonard. Professor Proton — real name: Arthur Jeffries — followed his TV career with private performances for kids parties, so he was surprised when he was hired by the guys to perform for them (and unhappy, at 83, about climbing all those stairs). Arthur later makes Sheldon jealous when he asks Leonard — and not Sheldon — to read a scientific paper he wrote, but the two makeup before Professor Proton dies in “The Proton Transmogrification.” Having inspired Sheldon to pursue a career in science, Professor Proton appeared in Sheldon’s dreams – in Obi-Wan Kenobi gear, complete with lightsaber — to remind Sheldon to appreciate the people he cares about before they die, and to stop wasting his life watching the same movies again and again. That last lesson doesn’t take, but producers have hinted Professor Proton could appear in Sheldon’s dreams once again … perhaps he’ll be provide the nudge Sheldon needs to make a proper effort at reconciling with Amy?

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Raj and Howard’s Bromance <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> They fight like a married couple and have gone to couples counseling together. They slept together naked (along with Sheldon) during a trip to the Arctic. And they briefly contemplated a group sex encounter (along with Leonard) with a visiting female physicist from Princeton. Yet despite the suspicions of everyone from Raj’s parents to Leonard’s mom that they are a romantic duo, Raj and Howard are simply BFFs who used to be each other’s wingmen and, now that Howard’s married, spend their time writing songs about Thor and Indiana Jones to perform as the two-man band called Footprints on the Moon.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Raj’s Skype Sessions With His Parents <span style="font-size:7.5pt;font-family:"Georgia","serif";mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:"TimesNewRoman";color:#111111"> Raj is the only character on TBBT who interacts with both his parents on a regular basis, and the only character for whom two parents have been introduced to viewers. Dr. and the former Mrs. Koothrappali check in with and up on their son via Skype sessions from India, where they fret about wanting grandchildren from him and the fact that he instead spends most of his time with “that Jewish boy,” i.e., Howard.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">The Relationship Agreement <span style="font-size: 7.5pt;font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> A 31-page document written by Sheldon and agreed to by Amy when they officially became boyfriend and girlfriend in season five’s “The Flaming Spittoon Acquisition.” The agreement is largely for Sheldon’s benefit, of course, though affection-craving Amy finds it romantic at first (and more important, binding). It establishes rules for hand-holding (initially allowable only if either party is in danger of falling off a cliff, had just won a Nobel Prize, or was afraid of getting a flu shot), date night (the second Thursday of every month), and what to do in the case of an intelligent dog uprising (says Amy, “We plan on selling out the human race hard!”). If a reconciliation between Sheldon and Amy happens in season nine, presumably, the Relationship Agreement will be heavily updated. And should a marriage ever occur … the most complicated prenup in the history of matrimony.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Restraining Orders <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Sheldon Cooper is nothing if not zealous about his interests. That’s why Stan Lee, Bill Nye, Carl Sagan, and Leonard Nimoy have had restraining orders against him.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Rock Paper Scissors Lizard Spock <span style="font-size:7.5pt;font-family:"Georgia","serif";mso-fareast-font-family: "TimesNewRoman";mso-bidi-font-family:"TimesNewRoman";color:#111111"> The guys’ variation on Rock Paper Scissors, used to make important decisions like what to watch on TV. The rules: scissors cuts paper, paper covers rock, rock crushes lizard, lizard poisons Spock, Spock smashes scissors, scissors decapitates lizard, lizard eats paper, paper disproves Spock, Spock vaporizes rock, and rock crushes scissors. And, yes, everyone chooses Spock most of the time.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">The Roommate Agreement <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Often the bane of Leonard’s existence, the exacting and minutae-filled Roommate Agreement is a document written, and frequently updated, by Sheldon, containing many clauses and riders about what is allowable and what is not regarding life in apartment 4A, as well as agreed-upon preferences for food and entertainment options. Among the more interesting rules: If Leonard ever develops superpowers, he must name Sheldon his sidekick; Leonard is not allowed to kill Sheldon if Sheldon ever becomes a zombie; Sheldon must ask Leonard how he is at least once a day; and Friday nights were reserved for watching Firefly, as Sheldon assumed the space Western would run for many years.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Sarcasm <span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111"> Sheldon didn’t understand it in the early seasons, and jokes — often ones at his expense — would have to be explained to him by Leonard and his other friends. As Sheldon has become more socially aware, and just plain sociable, he not only recognizes sarcasm but often is the one making sarcastic remarks — about Leonard’s shortness or lactose intolerance, Penny’s plethora of past boyfriends and lack of formal education, Raj’s lack of successful dating relationships, and Howard’s lack of a Ph.D. (Even though, as the only one of the four main male characters without one, Howard is the most successful scientist … he’s gone into space and worked with Stephen Hawking.)

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">The Schedule <span style="font-size:7.5pt;font-family: "Georgia","serif";mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family: "TimesNewRoman";color:#111111"> Sheldon’s life is rigidly planned from morning to night, from food choices to recreational plans, from wardrobe to bathroom times (his and Leonard’s while at the apartment). Examples: Monday is Thai takeout night, which means mee krob and chicken satay with extra peanut sauce, but no chopsticks; Tuesday is a barbecue bacon cheeseburger (with barbecue sauce, bacon, and cheese on the side) from the Cheesecake Factory, because Bob’s Big Boy serves a double-decker burger and TCF’s single-decker burger offers a “more satisfying meat-to-bun-to-condiment” ratio; and Friday nights are Vintage Game Night, plus Chinese takeout: chicken with broccoli with the chicken diced, not shredded, brown rice, not white, hot mustard from the Korean deli, and low-sodium soy sauce. Takeout options can be, and have been, altered, but only after a public meeting and a 60-day comment period, as per the Roommate Agreement.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Schrödinger’s Cat <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Austrian physicist Erwin Schrödinger’s thought experiment, which Sheldon uses in the season-one finale, “The Tangerine Factor,” to help Penny decide whether or not to turn her friendship with Leonard into a romantic relationship. The potential romance could be considered either a success or a failure until she actually pursues it, Sheldon explains, just as Schrödinger’s cat could be considered alive or dead until the box is opened. After kissing Leonard during the first date, Penny declares, “The cat’s alive!” Penny understands the theory well enough to try to explain it to another date in season two, while Sheldon applies Schrödinger’s Cat to his own friendship with Leonard in season five’s “The Russian Rocket Reaction.” In what he dubs “Schrödinger’s Friendship,” Sheldon is considering Leonard both his friend and his enemy, until Leonard makes a decision about attending a party at the home of Wil Wheaton, who was then on Sheldon’s enemies list.

<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto; line-height:normal"><span style="font-size:7.5pt;font-family:"Georgia","serif"; mso-fareast-font-family:"TimesNewRoman";mso-bidi-font-family:"TimesNewRoman"; color:#111111">Selective Mutism <span style="font-size:7.5pt; font-family:"Georgia","serif";mso-fareast-font-family:"TimesNewRoman"; mso-bidi-font-family:"TimesNewRoman";color:#111111"> Until the season-six finale, Raj suffered from selective mutism, a condition which prevented him from being able to talk to women, lest he imbibe copious amounts of alcohol. But in “The Bon Voyage Reaction,” a painful breakup with girlfriend Lucy — a woman whom he really liked but who suffered from more social anxieties than he did — finally helped him get over the mutism, which he discovered accidentally during a sober conversation with Penny.

He doesn’t usually drink, but on the rare occasions that he does enjoy an alcoholic beverage, he has been known to moon an awards-show audience (at which he was the award recipient), challenge Wil Wheaton to a fight, burp pi, and smack Amy on the tuchis (much to her affection-starved delight).

Oh, the Shenny shippers exist, as does their fanfiction. But while a romantic pairing between the characters isn’t likely to ever happen — and, we cannot stress strongly enough, never should — Sheldon and Penny have proven to be among the most fun pairings on TBBT, with fantastic comedic chemistry. From him trying to teach her physics and driving her to the emergency room when she fell in her bathtub to her gifting him with the greatest present ever (see Spock) and making him a fan of Long Island iced teas, the duo have forged a great affection and, begrudgingly on Sheldon’s part, respect for each other throughout the seasons. Penny is as charming and outgoing as Sheldon is awkward, and her Nebraska-grown common sense and people smarts can trump his supergenius brain at times. Like in season two’s “The Panty Piñata Polarization,” in which Penny uses a secret weapon — a call to Sheldon’s mother — to end a feud that began when he kicked her out of his apartment.

He loves them so much that one of the easiest ways to annoy him is to tell him you hate trains, as Raj tried to do when Sheldon wanted to bunk in Raj’s apartment temporarily. Sheldon is so obsessed with trains that having a train store nearby is one of the criteria by which he judges a city’s viability as a potential new home, and at the end of season seven, he took off on a long, soul-searching train trip when he hit a career speed-bump. Best train moment: season seven’s “The Locomotive Manipulation,” during which Sheldon kissed Amy for the first time — and liked it — during a Valentine’s Day dinner aboard a vintage train.

Can only be accurately described as a cross between a pant and a gasp, yet is nonetheless delightful.

Sheldon’s mother, Mary, describes his siblings — fraternal twin sister Missy and older brother George — as “dumb as soup,” but Missy, who made Sheldon an uncle during season seven, appeared to be more social, with a clever sense of humor, when she visited Sheldon in Pasadena in season one. She’s proud of, but not intimidated by, her twin’s intellect … especially since she knows she can threaten to inflict pain on his groin area to get him to do what she wants.

The left end of the living-room couch is Sheldon’s spot, and woe to anyone who dares sit there, as he has claimed “eternal dibs” on it. “In an ever-changing world, it is a single point of consistency,” he explains. “If my life were expressed as a function on a four-dimensional Cartesian coordinate system, that spot, at the moment I first sat on it, would be zero, zero, zero, zero.” Sheldon also tends to have a spot in other venues, including the Caltech parking lot, despite the fact that he doesn’t drive or own a car.

A short-sleeve T-shirt with a long-sleeve shirt underneath is the Sheldon Cooper uniform, but the pop-culture-themed tees have become a character trademark, depicting everything from various incarnations of the Flash, Superman, Batman, Green Lantern, Rubik’s Cube, Shazam, a TV test pattern, The Greatest American Hero, Aquaman, Rock ’Em Sock ’Em Robots, and Space Invader.

The sweet lullaby Sheldon’s mom used to sing to him when he was sick. He makes Penny sing it to him for the first time in season one’s “The Pancake Batter Anomoly” — after he teaches it to her — and he goes on to sing it himself for a sick Penny (including a version in a round) and an ailing Professor Proton. Everyone, now: “Soft kitty, warm kitty / Little ball of fur / Happy kitty, sleepy kitty / Purr, purr, purr.”

Hands down, Sheldon’s favorite Star Trek character — Spock’s commitment to all things logical resonates deeply with Sheldon, who watched the show as a child genius surrounded largely by people who thought he was a giant weirdo. One of the series’ greatest scenes — from season two’s “The Bath Item Gift Hypothesis” — revolves around Cheesecake Factory waitress Penny gifting Sheldon with a napkin used and signed by restaurant patron Leonard Nimoy. Germaphobe Sheldon isn’t at all grossed out by the soiled napkin. “I possess the DNA of Leonard Nimoy?” he shouts. “All I need is a healthy ovum and I can grow my own Leonard Nimoy!” Sheldon further ignores his aversion to germs and touching other humans when he gifts Penny with an awkward hug (and multiple bath-product gift baskets).

Nimoy’s son Adam, a TV director, author, and teacher at the New York Film Academy in Los Angeles, will guest-star in season nine’s “The Spock Resonance” episode of TBBT.

His friends seem financially comfortable enough to be able to indulge most of their pop-culture obsessions, but Raj can afford to go a little overboard on the gadgetry and collectibles because he has something Sheldon, Leonard, and Howard don’t: rich ’rents. Even after his purchase of a very expensive toy helicopter nearly caused them to cut off his generous stipend, he sweet-talked his divorced parents into instead actually increasing the allowance. Which means more gourmet dinners for Cinnamon.

The Star Trek: The Next Generation star has a long-running and complicated relationship with Sheldon, who, as a 15-year-old, spent ten hours on a bus — necessitating that he break his personal rule about urinating in a moving vehicle — just to get Wheaton’s autograph at a sci-fi convention. Wheaton never showed up (it’s later revealed that he chose to appear on an episode of Hollywood Squares instead), earning himself a choice spot on Sheldon’s enemies list. The two go on to compete against each other in a bowling tournament; Wheaton angers Sheldon by using his celebrity status to skip the line at a special Raiders of the Lost Arkscreening; and Sheldon drunkenly tries to fight the man he refers to as the “Jar Jar Binks of the Star Trek universe” after Amy feels insulted by Wheaton when he guested on an installment of “Fun With Flags.” In between, Sheldon and Wheaton have partied together at Wheaton’s house and Howard’s bachelor party, while the TNG alum also played Penny’s boyfriend in Serial Ape-ist 2. And, continuously playing a cheeky, pot-stirring version of himself, Wheaton produced a podcast episode about his movie collaboration with Penny, during which he encouraged an on-air tiff between her and Leonard. Wheaton’s return in season nine’s “The Spock Resonance” will mark his 11th appearance on the series.

In season four’s “The Zazzy Substitution,” Sheldon and Amy break up for the first time, when she suggests his research is not as significant as hers. He copes by acquiring 25 cats, including Zazzles, named for the fact that he is “so zazzy.” Shamy reunites, thanks to some help from Leonard and Sheldon’s mother, and the kitties are given new homes, but the episode proves what we should have guessed all along: Everything about Sheldon predicted he is a cat person.