Improvise

The beauty of roleplaying games is that you can try almost anything! When you describe an action not detailed elsewhere in the rules, the GM tells you whether that action is possible and what kind of test you need to make, if any, to determine success or failure.

The GM isn't obligated to give you the same deal again in the future, but the GM can formalize the ruling if it becomes popular enough.

A "called shot" is the classic example of an improvised attack. Before making an attack against a creature it can see, the attacker can specify one of the target's body parts (such as a hand, eye, tail, or tongue). If the attack deals enough damage to leave the target with 0 hit points, the target takes half damage instead (round down), and it permanently loses the specified body part. In most campaigns, only heroes and major villains ever make called shots.