The sense of vulnerability reaches a height once Crowley starts to crawl over him, and when he kisses the inside of Castiel's thigh, he sucks in a sharp breath. The skin there is so sensitive, and he ought not to want to let someone like Crowley have such access, but he's intrigued by Crowley's actions down there. His hands ball into fists when he feels Crowley's nose, and he has to convince himself to relax again as Crowley finishes his approach.

Uncurling his hands, he flattens them out against Crowley's chest, interested in touching him but unsure of how to start exploring.

"I liked that. What you were doing." Started to do. Almost did. Castiel's not great with social cues, but he thinks continuing to ramble would be a bad idea so he leaves it at that, and occupies his mouth somewhere else with a kiss to Crowley's shoulder.