The Big Bran Hypothesis

Plot Summary
Sheldon and his obsession for cleanliness breaks into Penny's extremely untidy apartment in the middle of the night to clean it up although this causes a disastrous effect.

Extended Plot
Penny asks Leonard to sign for a piece of furniture while she is out. It turns out the furniture is bigger than expected and after a having 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 woken up by sounds coming from outside of his bedroom. Realizing that the door is open, Leonard goes across the hall with his light saber to find 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 awakes 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. 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 is 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, then hugs him saying, "Were O.K." Later, the guys help Penny put together her Media Center, but get so focused on the task that they don't hear Penny when she comments that she's hot and is going to take off her clothes.

Trivia

 * We realize that Sheldon is allergic to bees for the first time.
 * This is the First Time we hear that Howard is allergic to peanuts.
 * We find out in this episode that Leonard has 2,600+ comic books on Superman.
 * We see the inside of Penny's apartment for the first time.
 * This is the first time we hear Raj sing.
 * We learn that Sheldon is a neat freak and has trouble understanding sarcasm.
 * What was actually said was "The force required to lift is reduced by the sine of the angle of the stairs, CALL IT 30 degrees, so about half." As it is an approximation, saying about half would be better than saying exactly half.

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?

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

Sheldon: Boy, I feel so good today, I'm going to choose from the lower fibre content end of the shelf, Hello Honey Puffs.

(Penny is yelling from across the hall)

Penny: 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 organisational 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