Sheldon: Excuse me. This is not about protecting my friend. Im a big fan of homeostasis. Do you know what that is?
Penny: Of course not.
Sheldon: Homeostasis refers to a systems ability to regulate its internal environment and maintain a constant condition of properties like temperature or pH.
Penny: Worst bedtime story ever!

Leonard: What am I supposed to do?
Penny: Err, keep your mouth off other women.

Penny: At one point, they had me figure out how to get a banana out of a puzzle box.
Leonard: Wait, Sheldon gave me a banana in a box. He was testing me, too.
Penny: Unbelievable.
Leonard: And how could a chimp even solve that? That was impossible.
Penny: Really? You couldn't get it out?

Sheldon: Woman, you are playing with forces beyond your ken.
Penny: Yeah, well your Ken can kiss my Barbie.

Sheldon: If you're going to replace Wolowitz, I need to know a little bit more about you.
Stuart: All right.
Sheldon: Wolowitz went to MIT. What's your educational background?
Stuart: I went to art school.
Sheldon: Equally ridiculous. Let's go.

Sheldon: How can she not be sure how she feels? You know, when I have a feeling, I know it. Trains? Love them. Swordfish. I love them, too. They're fish with a sword for a nose.

Sheldon: Leonard, the transformers teach us that things are not always what they appear to be. You know, like, a semi truck might be an alien robot, or someone in a romantic relationship might feel differently than they appear to.