The careless quirk of Crowley's mouth isn't fooling him, but he wisely doesn't mention it.

Aziraphael knows the next step; they've been at this point before so many times that he can almost feel Crowley's hands in his hair already. But much as he'd like to imagine that Crowley's never been gone at all, he knows that precise movements are nearly impossible right now. And yes - things are quite acceptable as they are - but he has a hand free.

A moment later, he pulls the band out himself, just in case.