Sheldon: Do you want to hear an interesting thing about stairs?
Leonard: Not really!
Sheldon: If the height of a step is off by as little as two millimeters, most people will trip.
Leonard: I don't care. 2 millime--? That doesn't seem right.
Sheldon: It's true. I did a series of experiments when I was 12. My father broke his clavicle.
Leonard: Is that why they sent you to boarding school?
Sheldon: No. That was the result of my work with lasers.

Sheldon: I have a masters and two PhDs. I should not have to do this.

Leonard: Wow, Penny, you're on fire!
Penny: Yeah, so is Sheldon!

Raj: I say we wait until he looks at us then laugh, like "Yes, you're a smart and strong competitor but we're also smart and strong and we have a reasonable chance of defeating you".

Penny: Yes, I know men can't fly.
Sheldon: No, no let's assume that they can. Lois Lane is falling, accelerating at an initial rate of 32ft per second, per second. Superman swoops down to save her by reaching out two arms of steel. Ms. Lane, who is now traveling at approximately 120 miles per hour, hits them, and is immediately sliced into three equal pieces.
Leonard: Unless Superman matches her speed and decelerates.
Sheldon: In what space, sir, in what space? She's two feet above the ground. Frankly, if he really loved her, he'd let her hit the pavement. It would be a more merciful death.

Leonard: Before you say anything, have you heard of Schrodinger's cat?
Penny: Actually, I've heard far too much about Schrodinger's cat.
Leonard: Good.
*Leonard and Penny kiss*
Penny: All right, the cat's alive. Let's go to dinner.

Leonard: Come on! We have a combined IQ of 360 we should be able to figure out how to get into a stupid building.
*Two girls selling cookies ring every bell, the door opens*
Sheldon: What do you think their combined IQ is?

Howard: Grab a napkin, homey, you just got served.
Leonard: That's fine, you win.
Howard: What's his problem?
Sheldon: His imaginary girlfriend broke up with him.
Howard: Been there!

Sheldon: How often does one see a beloved fictional character come to life?
Wolowitz: Every year at ComiCon. Every day at Disneyland. You can hire Snow White to come to your house. Of course they prefer if you have a kid.

Leonard: [to Howard and Raj] Sheldon is at the Cheesecake Factory. [On the phone with Penny] Just tell him to go home.
Penny: Well, he won't leave. He says he's afraid he'll pass out on the bus and someone will harvest his organs.
Leonard: [to Howard & Raj] He is paranoid and he has established a nest.

Penny: It is the things you love that make you who you are.
Wolowitz: I guess that makes me large breasts.

Penny: And what kind of doctor removes shoes from asses?

Mary Cooper: I'm sorry, did I start that sentence with the words, "If it pleases your highness?"

Howard: Don't you think I should answer the engineering questions? I am an engineer.
Sheldon: By that logic I should answer all the anthropology questions because I'm a mammal.

Sheldon: I read an article about Japanese scientists who inserted DNA from luminous jelly fish into other animals; and I thought "Hey! Fish night-lights".
Leonard: Fish night-lights.
Sheldon: It's a billion dollar idea, ssh!