Quote from Niles in No Sex Please, We're Skittish
Niles: Listen, this isn't an easy subject to broach, but is it possible you're in love with Frasier?
Roz: Absolutely not.
Niles: You sound sure.
Roz: I am sure. I mean, if I were going to fall for him it would have been two years ago when we slept together.
Niles: Well then, another theory I'd like to explore is... Whoa, back up! You and Frasier slept together?
Roz: He didn't tell you?
Niles: No! Well, I suppose it's only natural. When the wolf and the lamb work together, it's only a matter of time before the wolf gets his way. I hope you were gentle with him.