Crowley had gained one of Aziraphale's abilities (with rather embarrassing results) from a tea delivered to his door, which left the possibility that someone might have gained one of his abilities.

Just as he's wondering this, he sees Sam conversing with a pair of rats, and grins.

Sidling on up, Crowley gives a small wave.

"Y'know," he says, "Never met a rat who could say no to a ham sandwich."