Games often turn severed appendages and heads into items necessary to progress further. Appendages may vary from game to game and so may their uses. Nowadays, hands can be used as keys, eyes as flashlights and magical heads as weapons, that throw fireballs from their eyes. Picking up arms and legs and using them as a club is also quite common.
A few games like Severance allows the player to take any random body part lost by an enemy as a weapon.