[And this is Derek being shocked as hell. He shifts his weight, confused, and ends up saying the only thing he can think of.]

I knew you were a cat. Couldn't tell which one.

[There's still tension in his voice, but it's a different kind, now. There's nothing about Alex that says he's lying or hiding his true reaction, but Derek's having trouble believing it. No one's even okay with meeting a werewolf, let alone thrilled about it.

He has a hundred things he wants to say, to ask, but he holds back, uncertain. This has to be too good to be true.]

This isn't you playing 'get the psycho to drop his defenses and strike later,' is it?