it's when you whack an enemy stealthily

whenever you're not in a firefight with the enemy, or you can circle around and whack them while they thought you're elsewhere... in the middle of a firefight

enemies

So you can reduce enemies without getting overwhelmed by their number

anywhere there are enemies

1. crouch ( "C" on keyboard ) to move stealthily

2. get close to an unaware enemy, be careful of their awareness ( that arc white line on your screen )

3. press "F" to takedown