A prison guard puts three prisoners in one room. The prison guard tells them that he will put a hat on each of them. He said that one or more of them have a big red dot on them. All three hats had red dots on them though. He said to them that the first prisoner who tells the guard whether they have a dot on their hat or not will be free. If the prisoner is wrong, he is executed. The prisoners cannot and will not see their own hats or communicate with each other. One of the prisoners, a minute later, goes to the prison guard and tells him that he is sure that he has a dot on his hat. The prisoner is freed. How did he know? If you do know the answer, put it in a Spoilers text wrap.