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.

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: My point is, while you're spending all this time on your own, building computers or practicing your cello, what you're really doing is becoming interesting. When people finally do notice you, they're gonna find someone a lot cooler than they thought. And for those of you that were popular in high school, it's over, sorry. Thank you. Congratulations.

Mary Cooper: Raj is it? Still having trouble talking to the ladies? Because you know at our church we have a woman who's an amazing healer. Mainly she does crutch and wheelchair people. But I bet she'd be willing to take a shot at whatever third-world demon is running around inside of you.

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.