Dean's never seen the results of Castiel's defecation, just a couple of glimpses of him hunched over a pot or crouching over a little hole in the ground. When he found out that wasn't a navel he'd poked at when Cas was unconscious, he did one of those full-body heeby-jeeby things he does on the show sometimes that manages to be oddly endearing.

I so need to type up my notes on this for you.