Ducks don't make a habit of eating slithery things.

[So he saw a seagull eating an eel once and was traumatized for life, what about it.

Crowley pouts at that unspoken request, as if he has any right to horde the alcohol, but relents after a moment and stretches out to splash a little whiskey into Aziraphale's tea.]

Not the worst criterion, you have to admit. Oh, I've slept with a werewolf! [He grins, bright and a bit ridiculous.] So that's one for the folklore list. Haven't run into a vampire yet, bit of a shame, that.