The Big Bran Hypothesis

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

Summary
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; Raj saves the day.

Extended Plot
Penny asks Leonard to sign for a piece of furniture while she is out. It turns out the furniture is bigger than they had expected and after having a difficult time, they eventually succeed in getting it up to her apartment. While there, Sheldon sees that Penny's apartment is a complete mess and insists on tidying up. Penny returns soon after. 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 and finds out that Sheldon has used Penny's spare key to enter her apartment to clean. Although initially he is opposed to the idea, he eventually caves in and helps Sheldon clean. The next morning Penny awakens to find out that her apartment has been cleaned. Entering Sheldon and Leonard's apartment in a fit of rage, she demands her key back. Sheldon tells Penny that she might want to see a doctor about her snoring. Penny 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. Later, Penny runs into Rajesh in the hallway and talks to him about being upset over what happened (although he doesn't reply as he has ). 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  to avoid embarrassing himself. Later, Leonard tries to apologize with several referencing moments in history where  resulted in positive outcomes. Penny cuts him off,and  then hugs him saying, "We're okay". Later, the guys help Penny put together her, but get so focused on the task that they don't hear her when she comments that she's hot and is going to take off her clothes. Soon they get completely carried away and go to the dump to find better materials, leaving Penny to do it by herself and would possibly leave the guys completely embarrassed when they see that she's finished the job herself.

Quotes
Leonard: You convinced me. Maybe tonight we should sneak in and shampoo her carpet.

Sheldon: You don't think that crosses the 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?

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. [Tries to pick up a box and falls down] It's just a matter of... 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.

(The morning after Sheldon has cleaned Penny's apartment.)

Sheldon: I'm feeling so good today, I'm going to choose from the lower fiber end of the shelf. Hello, Honey Puffs.

Penny: (from across the hall) SON OF A BITCH!

Leonard: Penny's up.

Penny: YOU SICK AND GEEKY BASTARDS!

Leonard: How did she know it was us?

Sheldon: I may have left a suggestive organizational schematic for her bedroom closet.

Penny: LEONARD!

Leonard: God, this is gonna be bad.

Sheldon: Goodbye Honey Puffs, hello Big Bran.

Critics
"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

Trivia

 * 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 seen.
 * First time it's seen that Sheldon has possible and has trouble understanding.
 * Sheldon did not knock his now famous three knocks when he went to apologize to Penny.
 * The book that Leonard picks up in Penny's apartment after carrying up her furniture with Sheldon is
 * When putting Penny's furniture together Howard complains over 's pictographic representation-assemble manual and states that this is why doesn't have a space program. This was true when the episode was aired in 2007. It should be noted that Sweden later have got a highly developed space program.
 * 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 is a reference to DC Comics Green Lantern, a 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 &mdash; call it thirty degrees &mdash; so about half." Sheldon corrects him, "Exactly half." Let $$\angle_{\mathrm{stairs}} \equiv \theta.$$ $$\mathrm{Then,} \sin{\theta} \approx \sin{30^{\circ}} = 1/2$$ is what Leonard sought. Actually, it appears Leonard wanted to say $$\sin{\theta} \approx 1/2 \ (\mathrm{as} \ \theta \approx 30^{\circ}), $$ $$\ \mathrm{not} \ \sin{30^{\circ}} \approx 1/2,$$ but already interjected, thus, causing this blunder.
 * Leonard wielding a lightsaber as a weapon, upon hearing a noise is a hold-over from the Unaired Pilot.
 * Raj's name is revealed to be Rajesh Koothrappali for the first time.