"Ah, I find those books to be the best sort, personally," So the Headmaster had a collection of old, Dark, and dangerous, did he? How interesting, "They have the most interesting information in them. Nevertheless, it is prudent to respect others' property rights."
Particularly since old, Dark and dangerous things got snappy when one didn't.
"And your approach does sound like a most satisfactory way to acquire information." He agreed before moving a chess piece.