It seems you have us at a disadvantage. You know us, we barely know you.

[The Leviathan grin, just a bit more, shuffling through Castiel's memories again.]

Except, of course, we do. We know you as well as your angel does; every little fear and every little weakness.

[Castiel growls, just a little, the action not at all physical but still getting the point across to the creatures in his head easily enough. They just laugh and ignore him, continuing to taunt the demon.]

Why would we get another vessel? We like this one. All hyped up on soul-juice and nice and quiet. I think we'll keep him.