With Black Ops, you got crazy tomahawk kill videos. There's no tomahawk in Call of Duty: Modern Warfare 3, however. Instead we have the throwing knife filling that role. The potential for crazy kills is unchanged though, as you can see in the above video (via CVG).
The user-created clip highlights a completely improbable death by throwing knife after it bounces several times off of a hovering Osprey, only to fall straight down into the back of a camping sniper. That's the sweetest cherry on top imaginable: not only do you get to see this crazy feat of video game physics, you also get the satisfaction of knowing it sent a shameless camper to respawn oblivion.