John and Mary, rival treasure hunters, enter the treasure room. In the room are 5 identical closed cardboard boxes, placed conveniently in a circle. The treasure hunters cannot get close to or touch the boxes at first.

In one of the boxes there is a large jewelled crown, all the other boxes being empty. One of the treasure hunters will get first choice of a box, but will not get to open it immediately. When the first box has been chosen, three large guards (who know where the crown actually is) will walk directly to 3 of the empty boxes and jump on them, crushing the boxes completely to show that they are empty. The guards will never go near the chosen box under any circumstances. The remaining box will be given to the treasure hunter who did not choose.

The treasure hunters, having now been fully briefed on the procedure, are free to act. The first person to touch a box makes the choice.

John pushes Mary aside, and she falls to the ground clutching her ankle. John sprints off and touches a box.

Why is Mary now sitting on the floor laughing?

by Leslie Green