Knife Throwing is a warmup. Players stand in a circle. One person mimes throwing a knife at another person, who then claps his hands, as if he had grabbed the knife just before it hit him. That person then throws the knife at someone else.
Multiple knives can be thrown. The knives can also morph into other objects, such as kittens, bowling balls, and balloons.
The thrower can scream "Die!" in an intense voice. The catcher can yell "Not today!" in response.
Attentiveness, watching your scene partners, and reacting to everything in your space.