So, in the relatively new releas Killzone 3, there is a close quarters button option called 'Brutal Kill.' It honestly is just what it says on the tin. There are several different game animations for the brutal kill based on your position relative to the enemy, whether they have a helmet, are near objects, etc. Some of them are cooler than this one, but this was my first.
Yeah, he's stabbing him in the neck with a knife. Brutal.