At the start a sniper is seen placing his scope to his eye. This is wrong because to see through the scope you need to place you eye slightly behind the scope as recoil will push the rifle back into your eye.
In the beginning, we see through the scope of a man with a rifle targeting a head shot on a woman. It is then revealed that he is playing paint ball. Paint ball players are taught to never target head shots with paintball guns since they still have quite a bit of force behind them and could seriously injure or blind someone if shot in the head.