Castle: Suggests premeditation. She knew she was gonna kill him, so she booked the room anonymously.
Beckett: Yeah, but then why sleep with him? Why not just push him out the window?
Castle: Because she's a black widow... The coldest-hearted creature on Earth. She lures an unsuspecting male, takes him into her web, and then the moment they culminate, as soon as he feels the ecstasy of achieving his biological destiny, she opens up her jaws and eats him alive.
Ryan: I'm glad I'm in a healthy relationship.
Beckett: (smiles) Yeah.