Can you solve this puzzle?

Four people are sitting round a large square table, (one on each side). There is a large obstruction in the middle of the table which prevents each person seeing the person directly opposite them. They are then told to raise their hand if they can see AT LEAST one man. As it happens they are all men, so they... show more Four people are sitting round a large square table, (one on each side). There is a large obstruction in the middle of the table which prevents each person seeing the person directly opposite them. They are then told to raise their hand if they can see AT LEAST one man.

As it happens they are all men, so they all put their hands up. They are then asked to determine the sex of the person sitting opposite them. After a while, one of them successfully works out that the person opposite is a male.

How does he do it?

There are no other people in the room. No communication is allowed. No mirrors. In fact no trickery whatsoever.
Update: Sorry Charles but the two people who can see the person opposite you would also see you so they would put their hand up anyway.
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