There's an old logical paradox about the Spanish barber who shaves only the men in the village who do not shave themselves.
What about the barber, then?
You're supposed to think about it and get into an unresolvable dilemma. If the barber shaves himself, then he's one of the men he doesn't shave, so he's not shaving himself.
Unresolvable, that is, until you take into account that the barber could be a woman.