Beth Garner: Something's going on. You're sleeping with her, aren't you?
Nick: Why are you interested in her?
Beth Garner: My interest is in you, not her. She seduces and manipulates people. She'll do anything she can.
Nick: I thought you hardly knew her?
Beth Garner: I know the type. I'm a psychologist.
Nick: That means... you manipulate people too! You're a practicing psychologist. You're better at it than she is.
Nick: So where is this going?
Catherine: Ask me "What do you want from me Catherine?"
Nick: What the fuck do you want from Catherine?
Nick: What is this? Some kind of joke?
Nick: How did you feel when I told you Johnny Boz had died, that day at the beach?
Catherine: I felt somebody had read my book and was playing a game.
Nick: But you didn't hurt.
Catherine: No.
Nick: Because you didn't love him.
Catherine: That's right.
Nick: Even though you were fucking him.
Catherine: You still get the pleasure. Didn't you ever fuck anybody else while you were married, Nick?
Catherine: Somebody has to die.
Nick: Why?
Catherine: Somebody always does.
Gus: Everyone she plays with dies.
Nick: I know what that's like.
Dr. Myron: Do you believe Lieutenant Nilsen deserved to die?
Nick: I didn't know him well enough. I won't miss him.
Gus: Where in the fuck you've been? I went over to your place.
Nick: Easy, cowboy, easy. I wasn't there.
Gus: I went over last night, too.
Nick: No, I wasn't there either.
Gus: You fucked her? Goddamn dumb son of a bitch, you fucked her! Goddamn, you are one dumb son of a bitch.
Nick: Next time I'll use the rubber.
Gus: I don't buy it! There's gotta be somebody there, who knows whats going on.
Nick: I know what happened alright! Catherine told me and everything she said has checked out.
Gus: You've got Goddamn tweety birds flying around your head! You think the two of you will fuck like minks, raise rugrats, and live happily ever after.
Catherine: Got some coke?
Nick: I've got a Pepsi in the fridge.
John Correli: Did you kill Mr Boz, Miss Tramell?
Catherine: I'd have to be pretty stupid to write a book about killing and then kill him the way I described in my book. I'd be announcing myself as the killer. I'm not stupid.
Nick: What did Manny Vasquez call you?
Catherine: "Bitch" mostly, but he meant it affectionately.
Nick: So was she ever a suspect?
Sheriff: Nope! There was some talk, but it never panned out.
Nick: What kind of talk?
Sheriff: Girlfriend.
Nick: What he had a girlfriend?
Sheriff: No! She did! But like I said, it never panned out.
John Correli: Were you ever engaged in any sadomasochistic activity?
Catherine: Exactly what did you have in mind, Mr. Correli?
Nick: How's your new book coming along?
Catherine: It's practically writing itself.
Nick: I'm in love with you already, but I'll nail you anyway.
Nick: I'm working my ass off, I'm off the sauce, I even stopped smoking.
Beth Garner: How's not smoking?
Nick: It sucks.
Nick: What's your new book about?
Catherine: A detective. He falls for the wrong woman.
Nick: What happens to him?
Catherine: She kills him.
Nick: You wanna play hard, come on.
Answer: No definitive answer is given in the film. Catherine didn't need a reason for anything that she did. As for Beth, that was just a bonus, or a coincidence. It could be argued that Catherine targeted Beth, and Nick was just unfortunate to be involved with Beth.
ChristmasJonesfan