The year is—let us say—1170, and you are the leader of a city watch in medieval Persia. Patrolling the dangerous alleyways in the small hours of the morning, you and your men chance upon two or three shady-looking characters loitering outside the home of a wealthy merchant. Suspecting that you have stumbled across a gang of housebreakers, you order them searched. From various hidden pockets in the suspect’ robes, your men produce a candle, a crowbar, stale bread, an iron spike, a drill, a bag of sand—and a live tortoise. The reptile is, of course, the clincher. There are a...