In this episode, Sheldon cleans up Penny's messy apartment in the middle of the night causing Penny to blame Leonard.
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 in the hallway talks with Leonard 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 do it themselves. Since they are not physically strong and they have to use the stairs they have a hard time. 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.
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 coming into her place while she was sleeping. She demands Leonard 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. Penny tells Leonard to stay away from her, before leaving in fury. Leonard forces Sheldon to march over to Penny's door and apologize for what he did, Sheldon reluctantly goes over to Penny's door, and truthfully owns up and apologizes to Penny for cleaning up her apartment, before she slams the door in his face.
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 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.
- This is the first episode to be filmed digitally.
- This is the first time where Penny freaks out, Sheldon allergic to bees, Howard allergic to peanuts, Leonard owns 2600+ comic books, the inside of Penny's apartment, Sheldon's Obsessive-Compulsive disorder and his sarcasm blindness.
- The Big Bran Hypothesis on The Big Bang Theory Wiki
- The Big Bran Hypothesis at the Internet Movie Database