Dean went willingly, and managed to stifle a moan. He rested his hands on his thighs and sat back on his heels, his face open, watching Castiel's face with an eagerness he would've denied if asked.
His tongue sneaked out to wet his lips, another unconscious sign of eagerness he'd be embarrassed to admit. But it should have been clear to the angel just what Dean thought he was going to be doing there on his knees, and how much he desired it.