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: 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.

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: 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.

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?