Sheldon: My point is, I don't like when things change. So, regardless of your feelings, I would like you to continue dating Leonard. And also, while we're on the subject, you recently changed your shampoo. I'm not comfortable with the new scent. Please stop this madness and go back to green apple.

Raj: I'm telling you, if xenon emits ultraviolet light, then those dark matter discoveries must be wrong.
Sheldon: Yes, well, if we lived in a world where slow-moving xenon produced light, then you'd be correct. Also, pigs would fly, my derrire would produce cotton candy, and The Phantom Menace would be a timeless classic.

Leonard: What are you doing in there?
Sheldon: I'm making hydrogen sulphide and ammonia gas. Just a little experiment in pest control.
Raj: It's not gonna work, dude. I grew up in India, an entire subcontinent where cows walk in the street, and nobody has ever had a solid bowel movement.
Sheldon: Well, we'll just see how long you can hold out.
Raj: Well, we'll just see how your noxious gas fares against my cinnamon-apple-scented aroma therapy candles.
Leonard: Didn't you say you're making hydrogen sulphide gas?
Sheldon: Yes.
Leonard: Isn't that flammable?
Sheldon: Highly. Oh, dear. [explosion]

Sheldon: And then after dinner, we will have birthday coitus.
Penny: Do you think that will also be historically accurate?
Leonard: I assume like the rest of frontier life, it'll be exhausting and short.
Sheldon: You're exhausting and short.

Amy: Did the electricity go out?
Sheldon: I don't know what you mean by "electricity," ma'am. I am just a farmer boy living in a little house on the prairie.

Amy: Feel any better?
Sheldon: I feel terrible. Well, should we make love now?
Amy: How can you even think about sex?
Sheldon: Hey, I'm a man; I have annual needs just like anyone.

Sheldon: How are you feeling?
Amy: Ugh. My stomach aches, I got the chills, my mouth tastes weird, it hurts to swallow, and I've got a little double vision.
Sheldon: Yeah. I'm feeling better, too.

Sheldon: This is how you're going to entertain your little cousin and his friends? By lying to them?
Howard: How is this lying?
Sheldon: A magic show is an inherently deceitful proposition. This is an ordinary top hat. You've chosen that card freely. I do not have a set of lock picks lodged in my keister.
Raj: Can't you just enjoy the wonder, Sheldon? Why must you peek behind the curtain? Or up the butt?
Sheldon: If we poison the critical thinking faculties of children by telling them that rabbits come out of hats, then we create adults who believe in astrology and homeopathy and that Ryan Reynolds was a better choice for Green Lantern than lovable rogue Nathan Fillion.

Howard: She's actually been keeping herself busy doing wedding research for you.
Amy: Oh, she-she doesn't have to do that.
Howard: She wants to. After all, you were her maid of honor.
Amy: Sheldon, tell your funny story about pretzels.
Sheldon: Oh, right. Yeah, oh, yeah. Did you know that we've been thinking of having pretzels at our wedding? Hmm? No, no. No, no, no, no, no. I'm sorry. No, rhinos. We're having rhinos at our wedding.
No! (stammers) I got to go.

Sheldon: I'm gonna need some help. Someone baby-proofed the front door.

Sheldon: Okay, I'll use real people. Um, if a certain dog-like loyalty is useful, then it's Leonard, hmm? If, uh, having a PEZ dispenser filled with TUMS is an advantage, Wolowitz, yeah. If a best man with fake testicles hanging from his truck is important, well, then, my brother's back in the running.

Penny: He means he's writing a book.
Leonard: I do. It's something I've been thinking about for a long time. Yeah. It's about a brilliant physicist who solves crimes using science.
Sheldon: Oh, Leonard-
Leonard: It's not about you.
Sheldon: He probably has to say that for legal reasons.

Amy: Penny gets 20 points for the sewing kit.
Sheldon: Yeah, minus five, because this is mine.

Amy: Okay, what's the next test?
Sheldon: Loyalty. We need to choose someone who has our backs, someone who will keep our secrets even from each other.
Amy: Well, I don't have any secrets from you. Do you have secrets from me?
Sheldon: Yes. Oh, that has been weighing on me for years.

Sheldon: Howard, I've had my eye on this limited edition Swamp Thing, but now that I'm about to buy it, I'm having second thoughts. What do you think?
Howard: I don't know, Sheldon, it's pretty expensive.
Sheldon: Yes, but what if it will make me happy, you know, waking up and seeing it every morning for the rest of my life?
Howard: Really, a walking clump of swamp grass?
Sheldon: Yeah, well, Bernadette's no prize either!