Precision Damage

Precision damage is a special class of damage dealt by certain abilities. A rogue's sneak attack and a skirmisher's skirmish are both examples of abilities that add precision damage to an attack. As it represents added damage from targeting vulnerable spots on an enemy, there are some enemies against which said precision has no effect, and are thus immune to precision damage.
Precision damage can only be dealt to living creatures with discernible anatomies—undead, constructs, oozes, plants, and incorporeal creatures lack vital areas to attack, and are thus immune to it. Any creature that is immune to critical hits is not vulnerable to precision damage. A character must be able to see the target well enough to pick out a vital spot and must be able to reach such a spot in order to deal precision damage. A character cannot deal precision damage while striking a creature with concealment or striking the limbs of a creature whose vitals are beyond reach (unless said limbs possess vital spots of their own).