There is an isolated village. Everyone in this village has a dot on the back of his/her head. Each dot is either red or blue. If a villager finds out the color of the dot on the back of their head, they have to kill themselves. Villagers do not talk about the color of the dots on anyone’s head. So one day this stranger arrives in the village. He has NO dot on his head. He tells the entire village exactly one thing during his visit, “At least one of you has a red dot on the back of your head.” After the stranger leaves, villagers start killing themselves, and eventually, all of the villagers are dead.

The question is this: What new information did the stranger give the villagers?

And I really don’t know the answer.