The rules were simple: you walked up to the black box and chose which button to press. Either the red one or the blue one. The red one would mean you were going on a trip to visit a cake factory. The blue would mean you were going to the cup final. But when it was his turn, Noah saw something unexpected. There was a red and blue button, but also a third, green button. Nobody else had seen a green button. Even his teacher could not see one when she turned the box around. What did it mean? Was he imaginging it? What would happen if he pressed it?