I was a sixth-former when I decided to turn the school canteen into a joke people still retch about. I half-emptied a plastic bottle of milk, stuffed it with leftover meat from my lunch, sealed it tight, then hid it inside a heating vent with the help of a mate. The warm air ran over it night and day for weeks. By winter's end we were vibrating with anticipation. One lunchtime we pulled it out, wandered into the lower-school tables, twisted the lid, and ran. The smell hit before we reached the doors. Students surged for exits, hands over mouths. Teachers gagged. Several people were sick on the floor. We never got caught. But I still remember the sound of hundreds of bodies fleeing something I made.