Ragdoll

From TF2 Wiki

Ragdoll is a physics generated feature of the game. When a player is killed but not gibbed, his body and limbs will react in a realistic fashion depending on the velocity and direction of the impact. This feature does not add to the gameplay, but is highly amusing nonetheless. Certain attacks such as a headshot or backstab will result in a much more exaggerated ragdoll effect than usual depending on how they are performed.