Why is that barber question a paradox?

The barber is a woman is the answer to a trick question not a paradox. The question doesn't specify what the barber shaves. It could be that he shaves people's heads who do not shave themselves. A woman might also have a beard. I would say that the barber doesn't shave "themself", he shaves himself and in this way he is excluded from the limitations of "them". Hope you get it.