It was fortunate for Dean that he couldn't see the smirk. Feeling his reaction was more than enough, the way Dean's erection began to twitch in his palm, physical enough of a response to properly get his attention. He bent in, pressing his lips to Dean's ear, nibbling and sucking at the shell of it. He abused the same ear he'd bitten earlier, in just as tender a way, breathed out Castiel's words against it.

"I don't know what's so bad about being a dog, Dean. You get a master who feeds you, waters you, exercises you--gives you a warm bed to sleep in at night. It could be good for you. A comfortable, safe life, so long as you don't bite. If you bite, I have to put you down."

He stroked as he spoke, and withdrew his hand when he'd finished, using rough fingers to pull Dean's jeans down past his hips.

"If you bite, I have to put you down," he repeated, more firmly, before pressing two of his musk-scented fingers against Dean's mouth. "I'd get them good and wet, if I were you."