[After Ryan and Esposito catch a break in their case]
Castle: I've got a bad feeling about this.
Beckett: Are we really rooting against solving a murder?
Castle: Well, I don't want to shave my head! Do you?
Beckett: Why would I shave my head?
Castle: You're in on the bet, aren't you?
Beckett: Yeah, but I didn't realize-
Castle: [imitates electric razor]

[as Det. Beckett speaks with the victim's sister]
Castle: How does she do that?
Montgomery: Better than anyone I know.

[Beckett and Castle find the plastic surgeon's office; she and Castle walk past a well-endowed woman; Castle stares]
Beckett: Well, this must be the place. [clears throat] What is it with men and boobs, anyway?
Castle: Biological. We can't help it.
Beckett: But doesn't it bother you that they're so obviously not real?
Castle: Santa's not real. We still love opening his presents.

[Beckett has discovered who killed her mother, only to have to shoot him to save Castle's life]
Beckett: It wasn't your fault, you know.
Castle: I overstepped. I came down here to say that I'm sorry... and that I'm through. I can't shadow you any more. If it wasn't for me --
Beckett: If it wasn't for you, I would never have found my mom's killer. And some day soon I'm gonna find the sons of bitches who had him kill her. And I'd like you around when I do. And if you tell anyone what I'm about to say there's gonna be another shooting, but... I've gotten used to you pulling my pigtails. I have a hard job, Castle, and having you around makes it a little more fun.
Castle: ...Your secret's safe with me.

[Beckett's boyfriend Josh blames Castle for her getting shot]
Castle: He's right, you know. This is my fault.
Martha: Richard Castle, don't you dare blame yourself. You did not shoot her.
Castle: No, but I put her in the crosshairs.

[Beckett, Ryan, and Esposito are at dead ends in their respective cases]
Beckett: We'll start over. Fresh eyes. You take our murder, we'll take yours.
Esposito: All right.
Castle: [a thought strikes him] Whoa, whoa, whoa, whoa. Say that again.
Beckett: You take our murder, we'll take yours.
Castle: Could it be that easy? You take mine, I'll take yours.
Esposito: What are you getting at, Castle?
Castle: Strangers on a Train.
Ryan: The Hitchcock movie?
Castle: I'm partial to the novel by Patricia Highsmith, but yes. We have two strong suspects, but with airtight alibis, right?
Esposito: Right.
Castle: We know they're connected. What if the connection is the killers?
Beckett: Jason and Eric committed each other's murders.
Castle: And made sure they had an airtight alibi for the murder they knew they'd be suspected of. It's not our victims that are connected, it's our murderers. Crisscross!

[Castle enters the room, dressed as Mal from Firefly]
Alexis: Hey.
Castle: Hey... I was just trying on my Halloween costume.
Alexis: What exactly are you supposed to be?
Castle: Space cowboy.
Alexis: Okay. A: there are no cows in space. B: didn't you wear that, like, five years ago?
Castle: So?
Alexis: So, don't you think you should move on?
Castle: I like it.

[Castle has arrived late to a crime scene]
Esposito: Yeah, it's too bad, too. Your kind of case, bro'.
Castle: Yeah?
Ryan: Yeah, body was found down that manhole over there. Half eaten.
Castle: Eaten?
Ryan: Yeah, it was covered in some kind of green slime.
Castle: Whoa...
Esposito: Yeah, it was creepy. It's as if someone or some thing is down there.
Castle: [Catching on] Ha, that's... okay. Very funny. Great. [To Beckett] Was there a body down the manhole?
Beckett: Yeah.
Castle: Okay, thank you. An adult.
Beckett: Yeah, you should have seen what else was down there. Two metal canisters with bio-hazard stickers and yellow powder inside of them.
Castle: You opened the... [the detectives smirk] Alright. Will someone please tell me what's really going on here?
Ryan: We're gonna check nearby trash cans for the murder weapon.
Castle: What was the murder weapon, by the way?
Ryan: Some kind of death ray.
Esposito: Turns your insides out.

[Castle relates a traumatizing childhood experience that spurred him to become a mystery writer]
Castle: It must have just happened, because the tide hadn't washed away the blood. We had just played hide-and-go-seek the day before.
Beckett: What happened to him?
Castle: They never found out.
Beckett: I'm so sorry, Castle. [he smirks] ... you made that up?
Castle: It's what I do!
Beckett: You know what? You are so getting it for that one!

[Castle walks into the station carrying two coffees. Natalie is writing on the "murder board", Beckett eyes at her uneasily]
Natalie: [Takes a coffee] Thanks, Castle!
Castle: [Stunned at her audacity] Tha--that's, I was-- uh... you're welcome?
[Beckett looks shocked and distraught]
Castle: So, where are we?
Natalie: Ryan and Esposito are digging into Tanya Wellington.
Castle: [Directly addressing Beckett] Mmm, what about Duke Jones? Did his neighbour confirm his romantic evening?
Beckett: He--
Natalie: [Cuts her off] So did a couple of other neighbours, who complained about the noise. So it looks like Duke Jones allibis out.
Beckett: [Put out] What she said. [To Castle] Can we talk for a second?
Castle: Sure.
[Beckett loops her arm through his and quickly leaves the room, ending up frantically dragging him into another room]
Beckett: She took my coffee, Castle!
Castle: It's just coffee.
Beckett: Then what's next? My soul?! Everything I do, she does. Even when I'm thinking I can feel her in my head like some kind of a brain-eating parasite from one of her movies!

[Hans finds out Castle is not the person he was supposed to meet and grabs his shirt]
Beckett: NYPD! Hands up! [Castle puts his hands up] Not you Castle!
Castle: Right.

[hiding behind a kitchen island while getting shot at]
Beckett: [to Castle] Stay down!
Castle: You stay down!
Beckett: I can't shoot him from down here.
Castle: Yeah, and he can't shoot you either!

[M.E. Perlmutter eats his lunch on an examination table in the morgue]
Castle: Are you sure it's sanitary to be eating here?
Perlmutter: Do you know the strength of the disinfectants we use here? This is the cleanest room in the city. [offers his sandwich to Castle]
Castle: I couldn't.
Perlmutter: Homemade.
Castle: I couldn't.

[Natalie walks in dressed up as Beckett, with a brunette wig and similar suit. Castle's and Beckett's jaws drop.]
Castle: Just like I dreamed it! [They both stare at him] Did I say that out-loud?

[parked outside the home of a grandfather who killed his daughter's murderer]
Castle: You could just leave it like this. Sam's dead. The captain's happy. Those kids look pretty happy.
Beckett: That's the difference between a novel and the real world, Castle. A cop doesn't get to decide how the story ends.