There's a pause (not a very long one), in which Crowley realises quite quickly that if he follows Aziraphael down that path, he's almost certain to lose.

The thought itself doesn't seem to disturb him much - but on the other hand, it's a matter of principle.

Diversionary tactic: "I hope you brought enough books for all the reading you're going to be doing."

There aren't many other distractions in the immediate vicinity, after all, and almost none that don't involve venturing out into the direct sunlight.