Here's an easy riddle: You are in a room with 3 switches. The room is adjacent to another in which there are 3 lightbulbs. Each of the lightbulbs is connected to a switch in your room. You cannot see into the other room. You may manipulate the switches in any way you like, and you may go to the other room and observe the results, but only once (once you leave your room, you cannot reenter). How do you find out which switch leads to which bulb?