Leonard: Hey. Listen, since we got, you know, interrupted last night, I didn't have a chance to give you this.
Penny: Oh, Leonard, you shouldn't have. Oh, boy! What is it?
Leonard: It's a snowflake. From the North Pole.
Penny: Are you serious?
Leonard: Uh-huh. It'll last forever. I preserved it in a one percent solution of polyvinyl acetal resin.
Penny: Oh, my God. That's the most romantic thing anyone's ever said to me that I didn't understand.
Leonard: It's actually a pretty simple process. You see, cyanoacrylate are monomers which polymerize on... [Penny kisses him]

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?

Howard: Sheldon, you remember the first few weeks we were looking for magnetic monopoles and not finding anything, and you were acting like an obnoxious, giant dictator?
Raj: I thought we were going to be gentle with him.
Howard: That's why I added the '-tator'.

Sheldon: What are they doing here?
Leonard: We came to apologize again and bring you home. So why don't you pack up your stuff, and we'll head back?
Sheldon: No, this is my home now. Thanks to you, my career is over, and I will spend the rest of my life here in Texas trying to teach evolution to creationists.
Mrs. Cooper: You watch your mouth, Shelly. Everyone's entitled to their opinion.
Sheldon: But evolution is not opinion, it's a fact.
Sheldon's mom: And that is your opinion.

Sheldon: Hello Penny. I realize you are currently in the mercy of your primitive biological urges. But, as you have an entire lifetime of poor decisions ahead of you, may I interrupt this one?