Leonard: See? Now, that's the great thing. We're out as friends. This is not a date. Sex is off the table. So, let's go learn why hydroelectric power might not be the environmental bargain you think it is. Sorry. Spoiler alert.

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.

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

Amy: If you're keeping him, I've got a cage you can borrow. One of the test monkeys slipped on a banana peel and broke his neck. It was both tragic and hysterical.

Sheldon: Get back here, you stupid bird, so I can love you.

Penny: Really? On top of everything, you're afraid of birds?
Sheldon: Its called ornithophobia and someday it will be recognized as a true disability, and the landlord will be required by law to put a giant net over the building. Which is unfortunate because I have a fear of nets.