He knows. I don't know how he knows, but Klaus knows I'm human.
....And I realize I haven't actually told all of you that.
But I am. There was a cure. Elena forced it on me. And I was keeping it a secret since I got back but now he knows and I don't know what he might do. Truce be damned, I'm a commodity to him. And I doubt Elijah can keep him contained if he is so inclined to use me for something.