Crowley sighs happily at the gentle vibration that emerges from Aziraphale's throat. His purring isn't as pronounced in this form as it is when he's a cat, but it's still a happy noise, and he welcomes it. "Sounds good. In a diabolical 'You tempting fiend, how dare you offer me my heart's desire' way, of course."

Crowley has made it clear on any number of occasions that Aziraphale is welcome to tempt him. Also that he will very willingly give in. It does help that Aziraphale never tempts him with anything Crowley truly doesn't want or would be conflicted about, granted.