Penny: What about Howard and Raj? How did he become friends with them?
Leonard: I dunno. How do carbon atoms form a benzene ring? Proximity and valence electrons.
Penny: Sure, when you put it like that.

Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis?
Sheldon: Screwed?
Leonard: There you go.

Sheldon: This song is never going to stop. Have you ever dealt with something so relentlessly irritating?
Leonard: That's a trick question, right?

Leonard: Penny, as a scientist, my job is to figure out why things happen. But I don't think I'll ever understand how someone like me could get to be with someone like you. You know maybe I don't need to understand it, I just need to be grateful. I love you, Penny.

Sheldon: A fear of heights is illogical. A fear of falling, on the other hand, is prudent and evolutionary.

Wolowitz: *After he fixed Sheldon's algorithm* Gee, why can't Sheldon get a friend?

Sheldon: What part of an inverse tangent approaching an asymptote don't you understand?