Raj: You know, I just read a study that suggests new mothers are better at sensing emotions for up to two years.
Amy: It's true. Pregnancy causes physiological changes in the brain that result in increased empathy.
Penny: Huh. So all we need to do is get Sheldon knocked up.
Leonard: We can't. He was already fixed when I found him at the shelter.

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?

Leonard: He really worked with the Drug Enforcement Agency?
Penny: He didn't know it 'til he was cuffed, but yeah.

Amy: Well, everybody has things that they need help with. Like me. I can't see without my glasses. And right now you're just a cute, pink smudge wearing a childish green smudge.

Bernadette: You know, I just read that a team at MIT developed a device that helps people read human emotions.
Leonard: And you think we can get those guys to reprogram Sheldon? Cool.