He is expected to add something which is entirely unnatural, namely a kind of artificial demonstration of his emotions.

He must not only behave like an angry man, but he must behave like a man who is consciously interested in his anger and wants to demonstrate it to others.

He exhibits his emotions for the spectators.

He really acts theatrically for the benefit of the bystanders.

If he did not try to do so, his means of conveying a rich story and a real conflict of human passions would be too meager.