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The Big Bran Hypothesis is the second episode of the first season of the American sitcom The Big Bang Theory. This episode first aired on Monday, October 1, 2007.


Sheldon's obsession for cleanliness causes him to break into Penny's extremely untidy apartment in the middle of the night and clean it up. He then gets Leonard in trouble with Penny; however, Penny speaks to Raj who saves the day. Penny forgives Leonard.

Extended Plot[]

The Big Bran Hypothesis 17

Moving Penny's entertainment center.

The Big Bran Hypothesis

Leonard and his lightsaber.

Setting their dinner of Thai food, Sheldon gives the group a lecture of the use of the fork in Thai history. A little later, Penny talks with Leonard in the hallway about her work at The Cheesecake Factory. She then asks Leonard to sign for a piece of furniture while she is out. They also ask her if they want to join them later for Thai food and a Superman movie marathon. Penny is not sure how many there are, but she does like the one where Superman catches Lois Lane from falling. As Sheldon starts an argument on how that is impossible, Penny sneaks off to work.

It turns out the furniture is bigger than they had expected. The delivery man does not help them, so Leonard and Sheldon are forced to carry it up The Stairs the themselves since The Elevator doesn't work. Sheldon's only idea involves using a Green Lantern power ring. Finally, they eventually succeed in getting it up the stairs to her apartment. While there, Sheldon sees that Penny's apartment is a complete mess and insists on tidying up. But Leonard says that he should not do that because it is not their apartment. Penny returns soon after. She asks if they had any trouble and Leonard tells her no.

Leonard holds sarcasm sign

First time Penny goes ballistic! Sheldon cleaned her apartment.

Later that night Leonard is awakened by sounds coming from outside of his bedroom. Realizing that the door is open, Leonard goes across the hall with his lightsaber and finds out that Sheldon has used Penny's spare key to enter her apartment to clean. Sheldon couldn't sleep knowing that outside his bedroom was the living room; and outside the living room was the hallway; and immediately adjacent to the hallway was... this. Although Leonard is initially opposed to the idea, he eventually caves in and helps Sheldon clean to get him back.

Leonard get up the next morning and Sheldon tells him that he slept well. Leonard remarks that a well known folk cure for insomnia is to break into your neighbor's apartment and clean. Sheldon asks if that was sarcasm. Penny awakens to find out that her apartment in a well ordered state and screams about those geeky bastards. Penny charges into Sheldon and Leonard's apartment in a fit of rage about them coming into her place while she was sleeping. She demands her key back. Sheldon tells Penny that she might want to see a an otolaryngologist about her snoring. "It’s a throat doctor," he explains. Penny then asks Sheldon what kind of doctor would remove a foot from somebody's ass. Leonard holds up a sarcasm sign to let Sheldon know what Penny meant.


Leonard apologizing to Penny.

Later, Penny runs into Raj in the hallway and talks to him about being upset over what happened (although he doesn't reply as he has selective mutism). Penny decides to forgive them while Raj was thinking; "Boy, her hair smells nice" and "Maybe my mother was right. Maybe I should marry an Indian girl. We would have the same cultural background and she could sing the same lullabies my mother sang to me". Penny then hugs Raj, much to his surprise. He then turns his pelvis to avoid embarrassing himself. Later, Leonard tries to apologize with several analogies referencing moments in history where errors in judgment resulted in positive outcomes. Penny cuts him off, and then hugs him saying, "We're okay".

Later, the guys help Penny put together her media center, but get so focused on the task that they don't hear her when comments that she's hot and is going to take off her clothes. Soon they get completely carried away and go to the garbage dump to find better materials, leaving Penny to do it by herself and possibly leaving the guys completely embarrassed when they see that she's finished the job herself.



  • "A really enjoyable follow up to the pilot. Sheldon’s convictions create a plausible and funny source of conflict for the newly forming group of friends. The writers work really hard here to build a credible world for the characters which feels real and is funny. Long may it continue." - The TV Critic's Review
  • IMDb user reviews


  • Title Reference: The Big Bran is one of Sheldon's high fiber cereal. After cleaning Penny's apartment he feels a sense of accomplishment and opted to consume the Honey Puff cereal (Low Fiber) but after hearing Penny's frustrated yelling he settles for the Big Bran.
  • Chuck Lorre's vanity card.
  • This episode was watched by 8.58 million people with a rating of 3.4 (adults 18–49).
  • Episode transcript.

Costume Notes[]


Distressed Superman


Rainbow Bolts

Angled striped tee

Angled Striped


Unknown "fans" shirt

Sheldon wears multiple shirts in this episode, starting off with a worn (distressed) light blue shirt with a Superman logo and. When Penny's box arrives, Sheldon is wearing a multi-colored rainbow t-shirt. The next morning when Penny arrives angry that Sheldon entered her apartment, he can be seen wearing a blue t-shirt with angled green stripes. This shirt was originally available through Urban Outfitters but has been discontinued. By the final scene in Penny's apartment, Sheldon is wearing a white t-shirt with a pattern of multiple fans. Information on this item would be appreciated.




Leonard's APS shirt


Deter 3 Penguins

Leonard starts out wearing a black t-shirt with the molecular structure for caffeine. When Penny's box arrives, Leonard can be seen in a t-shirt from The American Phytopathological Society (a non-profit membership organization dedicated to plant pathology - they make their shirt available to the public, so please support them and buy a couple!). After the blow up with Penny, Leonard sports a black shirt with a wolf howling at the moon. As the guys discuss Penny's entertainment center, he wears a blue shirt with a blue maze pattern.


Bat buckle

The Euclid Alternative 12 - Nintindo

Nintendo Controller


Red/Black Vans


Green Lantern buckle

In the opening scene, Howard wears a white alien head pin, Batman cutout belt buckle, and yellow and black Vans shoes. As he dances to X-box, he wears a red alien head pin, red and black Vans shoes, and a Nintendo buckle. In the final scene in Penny's apartment, he has a Green Lantern belt buckle and has gone back to the yellow and black Vans.

Set Notes[]

Space Shuttle Atlantis
Spirit of St Louis
LogiTech iPod station

The model of the DC-7 on the bookshelves behind the couch has been replaced with a model of the space shuttle Atlantis (it turns up later in Leonard's bedroom). New items on the set include a Spirit of St. Louis radio and a LogiTech iPod Audio Station (model S-2017A ), both found on the shelves next to the front door.


  • First episode where Penny's sister and brother-in-law are mentioned.
  • First episode filmed after series was picked up.
  • Sheldon is wrong about the physics of pushing the furniture up the stairs. This is not just a question of work (energy) but also of power (energy/time). Since he and Leonard cannot produce an unlimited amount of energy per second (say), they may need to push it slowly, contrary to what he asserts. (This is a VERY serious and VERY basic error for a physics PhD!.)
  • As Raj searches for chop sticks, Sheldon educates the gang about chop stick use: they aren't to be used for Thai food, as Thailand has had the fork since the late 19th century; however, they typically don't use the fork to eat, but rather as a method to load food onto a spoon, which is used as a primary eating utensil.
  • First time it's seen that Sheldon is allergic to bees.
  • First time it's seen that Howard is allergic to peanuts.
  • First time it's seen that Leonard has 2,600+ comic books.
  • First time the inside of Penny's apartment is completely seen. In the pilot Penny is seen standing in it through the and the area around the door is seen from inside the apartment.
  • First time it's seen that Sheldon has possible Obsessive-Compulsive disorder and has trouble understanding sarcasm.
  • Sheldon did not knock his now famous three knocks when he went to apologize to Penny.
  • Sheldon states that he has got a master's degree and two PhD's though he does have more degrees.
  • The book that Leonard picks up in Penny's apartment after carrying up her furniture with Sheldon is 'The Secret' by Rhonda Byrne.
  • When putting Penny's furniture together Howard complains over IKEA's pictographic representation-assemble manual and states that these instructions are why Sweden doesn't have a space program. This statement was true when the episode was aired in 2007 when they did.
  • First time it's seen that Penny is shown to be a slob and has a temper.
  • Sheldon says, "Yes, but they all involve a Green Lantern and a power ring." This fact is a reference to DC Comics Green Lantern, a superhero and intergalactic police officer with a power ring that translates his ideas into green energy using the strength of his willpower and is charged by a Green Lantern Power Battery.
  • Leonard states, "Now we've got an inclined plane. The force required to lift is reduced by the sine of the angle of the stairs, call it thirty degrees, so about half." Sheldon corrects him, "Exactly half", upsetting Leonard. This conversation can be interpreted two ways:
    • Sheldon thought Leonard is claiming that the sine of thirty degrees is almost 0.5, whereas it is exactly 0.5.
    • Sheldon thought Leonard is claiming that by tilting the package, the force required to lift it is reduced by almost half (which is a correct assessment) but failed to grasp how exactly half (derived from the sine of thirty degrees) became almost half. In this case, Sheldon has neither realized that the angle considered by Leonard may be almost thirty degrees, nor takes the effect of friction into consideration.
  • Leonard wielding a lightsaber as a weapon and flashlight, upon hearing a noise is a hold-over from the Unaired Pilot.
  • Raj's first name is revealed to be Rajesh for the first time.
  • The Petre Devos picture by Xavier Allard in Leonard and Sheldon's kitchen appears for the first time. It would remain from this point on.
  • Arguments about Superman and his powers aren't new. Along similar lines, science fiction author Larry Niven did a great piece called  Man of Steel, Woman of Kleenex about the science and challenges surrounding sex between Superman and Lois Lane, as well as how Lois could survive a Kryptonian orgasm (the term "mind blowing" would have a whole different connotation if sleeping with the Man of Steel), or a surviving pregnancy with a super-baby inside her. Great food for thought and debate, from his book All the Myriad Ways.
  • Sheldon mentions the Mandelbrot Set of complex numbers. He's referring to a set of complex numbers; one "real", like normal numbers we're all familiar with, plus one "imaginary number", Imaginary numbers are needed because you can't do things like square a real number and get a negative number, or take the square root of a negative number and get a real number...thus i was invented. It is used extensively in complex functional analysis, in electronic and control engineering and in many other fields. Here, it allows the graphing of fractals and establishing magnitudes, rather than dealing with actual values. If you're interested in learning more about the Mandelbrot set, fractals, and chaos theory, try reading James Gleick's classic book  Chaos, Making new Science.


(The morning scene after Sheldon has cleaned Penny's apartment. He walks into the kitchen singing to himself and he stops singing when he sees Leonard)
Sheldon: Morning.
Leonard: (quite grumpy) Morning.
Sheldon: I have to say, I slept splendidly. Granted, not long, but just deeply and well.
Leonard: (so sarcastic at Sheldon) I’m not surprised. A well known folk cure for insomnia is to break into your neighbour’s apartment and clean.
Sheldon: Sarcasm?
Leonard: You think?
Sheldon: Granted, my methods may have been somewhat unorthodox, but I think the end result will be a measurable enhancement of Penny’s quality of life.
Leonard: You know what, you’ve convinced me, maybe tonight we should sneak in and shampoo her carpet.
Sheldon: You don’t think that crosses a line?
Leonard: Yes! For God’s sake, Sheldon, do I have to hold up a sarcasm sign every time I open my mouth.
Sheldon: You have a sarcasm sign?
Leonard: (very fed up) No, I do not have a sarcasm sign

Raj: Are there any chopsticks?
Sheldon: No need for chopsticks, this is Thai food.
Leonard: Here we go.
Sheldon: Thailand has had the fork since the latter half of 19th century. Interestingly, they don't put the fork in their mouth; they use it to put the food on a spoon which then goes into their mouth.
Leonard: (To Raj) Ask him for a napkin, I dare you.

(While trying to figure out how to get box with furniture to Penny's apartment)
Leonard: We don’t need strength, we’re physicists. We are the intellectual descendants of Archimedes. Give me a fulcrum and a lever and I can move the Earth, it’s just a matter… (starts to move package) I don’t have this... I don’t have this I don’t have this.
(Sheldon catches Leonard and the box)
Sheldon: Archimedes would be so proud.

Sheldon: Ah, gravity, thou art a heartless bitch.

Penny: Hi
Leonard: Oh.
Penny: What's going on
Leonard: Um, here’s the thing. (Reads from note.) Penny. Just as Oppenheimer came to regret his contributions to the first atomic bomb, so too I regret my participation in what was, at the very least, an error in judgement. The hallmark of the great human experiment is the willingness to recognise one’s mistakes. Some mistakes, such as Madame Curie’s discovery of Radium turned out to have great scientific potential even though she would later die a slow, painful death from radiation poisoning. Another example, from the field of ebola research….
Penny: Leonard
Leonard: Yeah.
Penny: (hugs him) We're okay.
(Kisses him on cheek. Closes door. Leonard looks happy, walks back across hallway and straight into the apartment door.)

(The morning scene at Apartment 4A after Sheldon asks Leonard that does he want any cereal)
Sheldon: I'm feeling so good today, I'm going to choose from the lower fiber end of the shelf. Hello, Honey Puffs.
(We now hear Penny shouting angrily from across the hall)
Penny: (out of vision) SON OF A BITCH!
Leonard: (nervous) Penny's up.
Penny: (out of vision) YOU SICK, GEEKY BASTARDS!
Leonard: How did she know it was us?
Sheldon: I may have left a suggestive organizational schematic for her bedroom closet.
(We now hear the angry Penny shouting from the hallway for the final time)
Penny: (out of vision) LEONARD!
Leonard: God, this is gonna be bad.
Sheldon: (He puts the packet of Honey Puffs back on top of the fridge) Goodbye, Honey Puffs. (he punishes himself into picking a packet of Big Bran) Hello, Big Bran.
(Sheldon admires the packet when there is a banging sound of door opening in the background).

(The scene of which Penny immediately bursts into Apartment 4A. she is furious)
Penny: (she's shouting at Leonard) You came into my apartment last night when I was sleeping?
Leonard: Yes, but, only to clean.
Sheldon: Really more to organise, you’re not actually dirty, per se.
Penny: (she's so very cross with Leonard) Give me back my key.
Leonard: I’m very, very sorry.
Penny: (she's asking Leonard crossly) Do you understand how creepy this is?
Leonard: Oh, yes, we discussed it at length last night.
Penny: (she's explaining angrily) In my apartment, while I was sleeping.
Sheldon: And snoring. (Penny glares at Sheldon) And that’s probably just a sinus infection, but it could be sleep apnoea, you might want to see an otolaryngologist. It’s a throat doctor.
Penny: (she's asking Sheldon crossly) And what kind of doctor removes shoes from asses?
Sheldon: Depending on the depth, that’s either a proctologist or a general surgeon. (Leonard holds up a sign reading “Sarcasm”) Oh!
Penny: (she is so mega-fully cross) God!
Leonard: Okay, look, no Penny, I think what you’re feeling is perfectly valid, and maybe a little bit later today when you’re feeling a little bit less, for lack of a better word, violated, maybe we could talk about this some more.
Penny: (she loses her hugest temper) Stay away from me.
Leonard: Sure, that’s another way to go.
Sheldon: Penny, Penny, just to clarify because there will be a discussion when you leave, is your objection solely to our presence in the apartment while you were sleeping, or do you also object to the imposition of a new organisational paradigm.
(The really bad tempered Penny stares in disbelief, then leaves.)
Sheldon: Well that was a little non-responsive.
Leonard: You are going to march yourself over there right now and apologise. (Sheldon laughs.) What’s funny?
Sheldon: That wasn’t sarcasm?
Leonard: No.
Sheldon: Wooh, boy, you are all over the place this morning. (Knocks on Penny’s door.) I have a masters and two PhD’s, I should not have to do this.
(Penny opens her apartment door. She is still very cross indeed)
Penny: (she shouts angrily at Sheldon) What?
Sheldon: I am truly sorry for what happened last night, I take full responsibility. And I hope that it won’t colour your opinion of Leonard, who is not only a wonderful guy, but also, I hear, a gentle and thorough lover. (Penny closes door in his face.) I did what I could.

(the corridor scene of Raj running up the last few stairs with a take-out in his hand and stops himself when he sees the so really upset Penny arriving down the last few stairs in a temper holding a basket of laundry)
Penny: (she greets Raj crossly) Hey Raj. (Raj stands looking uncomfortable. He walks a pace just as Penny faces Raj and she shouts at him about Leonard and Sheldon's folly) Hey, listen, I don’t know if you heard about what happened last night with Leonard and Sheldon, but I’m really upset about it, I mean they just, they let themselves into my place, and then they cleaned it, I mean can you even believe that? How weird is that?
Raj (voice-over): (internally, while Penny continues to talk) Ooh, she’s standing very close to me. Oh my, she does smell good. What is that, vanilla?
Penny: (she is still really very cross) You know, (she slams her laundry basket down onto the stairs in fury and she continues to shout at Raj) where I come from, someone comes into your house at night, you shoot, okay? And you don’t shoot to wound. I mean, alright, my sister shot her husband, but it was an accident, they were drunk. What was I saying?
Raj (internally): She’s so chatty. Maybe my parents are right. Maybe I’d be better off with an Indian girl. We’d have the same cultural background, and my wife would sing to my children the same lullabies my mother sang to me.
Penny: It’s obvious that they meant well, but I’m just, I’m having a really rough time, like I said, I broke up with my boyfriend, and it’s just freaking me out.
Raj (internally sings an Indian lullaby.)
Penny: I mean, just because most of the men I’ve known in my life happen to be jerks, doesn’t mean I should just assume Leonard and Sheldon are. Right?
Raj (internally): She asked me a question. I should probably nod. (Does.)
Penny: That’s exactly what I thought. Thank you for listening. You’re a doll. (She hugs him.)
Raj (internally): Oh-oh. Turn your pelvis. (Does.)