The look on Crowley's face is one of extreme dubiousness. Aziraphale could be explaining a part of the ten commandments that were rewritten for the modern audience and Crowley would have a similar, uncertain expression. He doesn't really like food all that much on his own, but there's something very wonderful and special about sharing food with Aziraphale, and that really is moments like this, where he's being extremely excited about it in ways that Crowley just isn't.

One can't be around someone as excited about food and not feel a little excitement themselves.

"All right, so this is one of the rolls---" Crowley says, pointing at one of the eel. He reaches out to take one, carefully.