That actually knocks the breath out of Castiel, but he doesn't so much as flinch. "If you devoured it, where do you think it went?"

Cas pushes a finger against the Leviathan's chest. "In here. Each of you got a speck; it's what makes you invulnerable. But you don't know how to use it, and I do." Cas lowers his hand.

Lying is...surprisingly easy as a human. But Castiel can't try to bluff his way out of this by being threatening; there's too good a chance the Leviathan will take the chance, and then Castiel is dead. He has to figure out something else.