At the Caltech cafeteria, the peach cobbler tastes like it's made of actual pieces of shoemaker which amuses Sheldon. Raj brings by his sister, Priya. She has a one-day layover in Los Angeles on the way to Toronto. Leonard and Howard had agreed not to hit on Raj's sister, though Leonard and Priya did have a history together and it quickly heats up on her return to America.
In the morning, after a lovely night with Priya, Leonard wonders if he should get a job in India so that they could date. Priya doesn't feel that that is a good idea since her parents prefer her with an Indian man. Still trying to hide from Sheldon, Leonard tries to distract him, but he still catches her walking out. Leonard then asks Sheldon to conceal his violation of a 2005 pinkie swear with Howard.
For Sheldon to keep a secret he must come up with a logical alternate explanation. He lies that Leonard went to a local Irish bar and hooked up with the fun loving and morally loose Ms. Maggie McGarry. She works at Lucky Baldwin's tending bar with a head full of curls and a heart full of dreams. Sheldon even has a phone number, an automated message and a lock of Maggie's auburn hair... from an orangutan.
Raj first worries about Priya ever being attracted to Howard and then asks Leonard about the new episode of "Caprica" which he missed due to his night with Priya. Leonard tries the Maggie McGarry alibi, but end up telling the truth. He admits to Raj he slept with Priya with both Howard and Raj going ballistic. After Leonard told him he offered Priya his heart and she stepped on it, Raj felt much better. Then everyone starts exposing and confessing things better left unsaid such as Howard dropping Raj's IPhone into a urinal, Howard lying to Raj about foreigners giving present to Americans on Thanksgiving and washing their clothes on the 4th of July, Sheldon grinding up moths and mixing them in Leonard's food as an experiment, and Raj using Sheldon's toothbrush (much to Sheldon's disgust and horror). He nearly breaks his friendship with Raj, but forgives him when he learns that Raj bought him a talking Thomas the Tank Engine.
Finally, Sheldon preparing snow cones and serving one to Leonard, and confessing they were made with mango caterpillar. Leonard then spits out the snow cone and leaves the apartment, upset.
- Guest starring:
- Teleplay: Bill Prady, Eric Kaplan & Maria Ferrari
- Story: Chuck Lorre, Lee Aronsohn & Steven Molaro
- TV Critic: "Bringing in family members is almost always a good idea in sitcoms as it helps root that character in a real relationship we can all relate to. The writers did nothing with Priya but she may come back one day. Her leap over the couch to hide from Sheldon was a nice visual gag...Raj's sister comes to town, she sleeps with Leonard who is betraying Howard by doing so. Who was the plot focused primarily on though? Yes that's right, Sheldon ...Feed Sheldon. Feed Sheldon. Feed Sheldon."
- The A.V. Club gave this episode a C.
- IMDb user reviews
- Title Reference: The Irish Pub that Sheldon included in the details of the deception to cover up Leonard's sleeping with Priya.
- Chuck Lorre's vanity card.
- This episode was watched by 13.04 million people with a rating of 4.2 (adults 18-49).
- This episode aired in Canada on October 28, 2010 with 3.204 million viewers and a weekly ranking of #1.
- In the United Kingdom, this episode aired on December 9, 2010 with 0.786 million total viewers and a weekly ranking of #2.
- In Australia, it aired on February 15, 2011 with 0.958 million viewers.
- Episode transcript 
- Leonard wears his Ames Brothers "Wisdom" shirt (the owl)..
- Neither Penny, Bernadette or Amy feature in this episode. Penny isn't mentioned, as the writers wrote her out of this and the previous episode after Kaley Cuoco broke her leg in a horseback riding accident. There is no regular appearance by Melissa Rauch as a main cast member in this episode and there is no guest appearance by Mayim Bialik in this episode. They are not featured in the next episode (S4E7) either. There are no on-screen appearances by them in any scene of this episode. They are not included in any of the story lines of this episode and there is no mention of them either.
- Sheldon's inability to keep a secret and his tendency to exaggerate lies were previously explored in "The Bad Fish Paradigm" (S2E1) and "The Loobenfeld Decay" (S1E10).
- The second of two Season 4 episodes where Kaley Cuoco (Penny) is absent, fourth of nine Season 4 episodes where Melissa Rauch (Bernadette) is absent, and the third of nine Season 4 episodes where Mayim Bialik (Amy) is absent.
- Thomas the Tank Engine was shown in Penny's apartment before (See "The Terminator Decoupling": S2E17), but this time is the first time it is referenced in the show.
- The "classic text-based computer game from the 1980s" that Sheldon plays, although unnamed in the show, is very likely to be Zork - which is characterized by the using of commands with prepositions, e.g. the command "hit troll with axe". Also, Zork is mentioned to be Sheldon's favorite in "The Hofstadter Isotope" (S2E20) and "The Toast Derivation" (S4E17).
- Sheldon has a thermal fluctuations|thermodynamic fluctuations seminar the day after Priya spent the night with Leonard.
- Priya's first appearance in the series, although it is claimed they all met before "Pilot".
- In the car, Leonard says, "Okay fine, I’m, I’m a horrible human being, I’m the Darth Vader of Pasadena." He was compared to Darth Vader while likewise driving the car, in "The Large Hadron Collision". Sheldon retorts, "You’re far too short to be Darth Vader. At best you might be a turncoat Ewok." Darth Vader is 6'8" (2.03 m), an Ewok is about 3'3" (1 m), and Leonard is 5'5" (1.65 m).
- Leonard is one thirty-second Cherokee Native American.
- Sheldon explains to Raj, "But that behavior is beyond the pale and cannot be tolerated. We are no longer friends." In "The Friendship Algorithm", Sheldon similarly remarked to Raj, "Maintaining five friendships promises to be a Herculean task. So, I’m going to have to let one of you go... Raj, you’re out." In both instances, he almost immediately rescinded his decision.
- It's as if Sheldon really did come with a manual (S1E16-"The Peanut Reaction"), as Leonard is able to repeat Sheldon's words about hating fun without even being present when he said it. Sheldon also made this evident in "The Bozeman Reaction" when he said on two occasions, "As you know, I’m not comfortable with prolonged good-byes and maudlin displays of emotion, so I prepared [a] short video."
- Sheldon recalls April 12, 2005 at a Bob's Big Boy, which was a Tuesday. This detail is consistent with his old schedule of going to Bob's Big Boy on Tuesdays as revealed in "The Hamburger Postulate".
- Despite Howard complaining about the cobbler, he continues eating it while Sheldon explains "Train Day".
- The mythical Maggie's hair sample came from a lab orangutan.
- Sheldon has an oddly shaped uvula.
- Second episode where a main character's sister comes to Pasadena and her attractiveness causes problems. First was "The Porkchop Indeterminacy".
- This is the only episode of the entire show without all three female members of the gang (Penny, Bernadette and Amy).
- Aarti Mann made her debut in this episode as Priya Koothrappali.
- Priya does more phyiscal comedy and seems less serious than in later episodes.
- Sheldon: You know I can't keep a secret!
- Leonard: You can if you try. Think about it this way: if I were Batman and you were Alfred Pennyworth|Alfred, you'd keep that secret, right?
- Sheldon: Why do you get to be Batman?
- Leonard: Because the Batman has the secret.
- Sheldon: Alfred has secrets, too!
- Leonard: Like what?
- Sheldon: Alfred knows that Barbara Gordon is Batgirl. Which I've now just told to Batman! See, I cannot keep a secret! The fun starts with brunch at Carney’s in Studio City, a hot dog stand in a converted railroad dining car. Next stop, Travel Town, an outdoor museum featuring 43 railroad engines, cars and other rolling stock from the 1880s to the 1930s. Finally, we’re off to the glitz and glamour of Hollywood for dinner at, that’s right, the Hollywood Carney’s, a hot dog stand in a different converted railroad dining car.
- Sheldon: You've asked me to lie on your behalf, and as you know, I am deeply uncomfortable with impromptu dishonest, so I've provided you with an iron clad alibi. You couldn't have spent last night with Priya, because you were with another woman.
- Leonard: Oh, I’m so sure I’m going to regret this, but, who was I with?
- Sheldon: The fun loving, and morally loose, Miss Maggie McGeary.
- Leonard: Oh, God.
- Sheldon: You met her at Pasadena’s most popular Irish watering hole, Lucky Baldwin’s, where Maggie spends her nights tending bar, with a head full of curls and a heart full of dreams.
- Leonard: (reading a napkin Sheldon has handed him) Leonard, call me if you’re interested in coitus. Sincerely, Maggie McGeary.
- Sheldon: And if anyone were to actually call that number they will hear this.
- Mechanical voice on Sheldon’s phone: Top of the morning to you. You've reached Maggie McGeary. Leave a message after the wee little beep.
- Sheldon: It’s pretty convincing, huh? And it wasn't even a real person. And here is the clincher. A lock of Maggie’s flaming auburn hair.
- Leonard: Where did you get that?
- Sheldon: From an orangutan in the primate lab.
- Leonard: An orangutan?
- Sheldon: Well, no-one’s going to run a DNA test on it, Leonard, honestly you over-think everything.
- Howard: Raj, I just want to say that I would never betray your trust. Unlike Leonard, I respect you.
- Leonard: Really? Was it out of respect that you didn't tell Raj about the time you dropped his iPhone in a urinal?
- Raj: Dude, I put that thing on my face!
- Sheldon: I think a more amusing violation of Raj's trust is when Howard convinced him that foreigners give presents to Americans on Thanksgiving.
- Howard: Hey, I didn't see you giving back your Snoopy snow cone maker!
- Raj: That was all a lie? This year's gifts are already wrapped!
- Howard: And as long as we're talking about betraying our friends, how about the month Sheldon spent grinding up insects and mixing them into Leonard's food?
- Sheldon: Excuse me! That was not a betrayal. That was an experiment to see at what concentration food starts tasting... mothy.
- Leonard: You put moths in my food?!
- Sheldon: For science!
- Raj: I can't believe you kissed my sister with moth mouth!
- Leonard: I can't believe you used Sheldon's toothbrush!
- Sheldon: You used my toothbrush?!
- Raj: Not the brush part! Just the little rubber thing to pick food from my teeth and massage my gums.
- The Big Bang Theory - The Irish Pub Formulation (TV Episode 2010) - IMDb
- The TV Critic's Review
- The Big Bang Theory: "The Irish Pub Formulation" - TV Club - The A.V. Club
- Thursday Final Ratings: Grey's Anatomy, Big Bang Theory, Shrekless, Office Adjusted Up; Nikita Down; Plus World Series Game 2 - Zap2it
- Top Programs – Total Canada (English) October 25 – October 31, 2010 - BBM Canada
- BARB via Wikipedia
- Week 8 - TV Tonight