You have probably noticed that your sights turn red from time to time, just for a couple seconds. Well, there is a reason for that: It means there is an enemy in front of you and if you pull the trigger when the sights turn red, you hit him. This applies both to aim mode (which you activate by pressing the right mouse button) and regular mode. When your sights start to glow red, pull the trigger – it is a visual clue that you can hit the enemy. It does not guarantee that you will score, for example, a headshot, but it guarantees that you will damage your opponent. If you are having trouble shooting your enemies, watch out for this visual clue.