"There is a programming in my head to kill Dean," Castiel confirms quietly, eyes dropping down to the floor as he remembers precisely the way he was trained to snap his neck, precisely how much pressure it would take. Clean and efficient.

"I don't why or when it was put there but it's there. I don't what else haven't remembered, yet. Measures need to be put in place in case I am ever out of control, but Dean and I do have some restrictions about who can be involved and what can be done. We are not willing to go to some extremes that would leave permanent damage."