It really bugs me when people on MN talk rubbish, and when they don't know simple science - and I KNOW everyone in the country has been taught this, as it is in the GCSE double award, which is the minimum amount of science that is compulsory in England.
It is called fright, flight or fight.
After a scare or injury, you are flooded with adrenalin, which is a hormone that diverts blood from digestion, immune system and other non critical systems. Blood rushes to heart and lungs, getting oxygen into muscles double speed, giving you more power and strength short term than your body can sustain longer term. You don't feel pain, you feel energy and aggression.
Yes, if you are shot in the ear, you first and most natural response is likely to be defiance and retaliation, pushing away security, ignoring danger, gestures of defiance or triumph.
I don't like the man, and I may even be a little bit sorry he wasn't hurt worse, but his reaction is not "unnatural" or "looks staged" or "obviously planned and acted" -on the contrary, it is entirely as you would expect.