Well, Aziraphale has never even so much as pretended not to be predictable. One develops habits after millennia on Earth. Crowley likes that, he thinks -- that ninety-nine point nine nine nine repeating percent of the time, he knows where to find Aziraphale.

Anyway. Yes, Aziraphale's in the library, in what he has personally deemed its comfiest (and, crucially, also its coziest) armchair. He's paging, with a skeptical look on his face, through a rather flimsy volume that has Practical Exercises for Young Magicians, by Amelia Popper stamped into its spine.