A natural weapon represents the weaponry that various creatures have as part of their bodies, used when unarmed strike is inadequate. These are usually implemented as creature weapons (claw, bite, gore, and slam), although the game allows any weapon to be used. Items that were created specifically for use as natural weapons are found in the creature item blueprint category in the Toolset.
Natural weapons receive special treatment when trying to overcome damage reduction. A creature who uses natural weapons and has damage reduction is able to pierce (ignore) damage reduction of the same power level as its own, even when the creature weapons have no attack or enhancement bonuses. For example, the claw attacks of a creature with 10/+5 damage reduction will not be affected by others' damage reduction of X/+5 or lower.
Every creature has three "creature" inventory slots for its natural weapons, called either "left", "right" and "bite" (in NWScript) or "claw 1", "claw 2", and "special attack" (in the Toolset). If a creature has no weapon in the main hand slot and no gloves in the gloves or bracers slot, then the creature will use its natural weapon(s) for combat. It is only when the creature has no natural weapons (or has gloves equipped) that it will resort to a true unarmed strike. (This distinction is important in some circumstances, such as when weapon-specific feats like weapon focus come into play.) When natural weapons are used in combat, most attacks will make use of one of the "claw" slots (evenly split between the two), with the remainder (less than a third of the time) using the "special attack". Which attack is used is random and does not depend on the number of attacks per round. In particular, if a creature has three natural weapons, all three will potentially be used in combat, even if the creature has but one attack per round.
The creature slots have different functionality than the weapon slots. While both can be used in combat, items in the creature slots cannot be disarmed (as these items represent innate abilities, even if the actual item in the slot happens to be, for example, a spear). Furthermore, the base damage of natural weapons is ignored; instead the "monster damage" item property (only available on creature weapons) determines the base damage of attacks. The keen property of natural weapons is also ignored, and the weapon's threat range and modifier are overridden to 20/x2. The type of weapon is ignored with regards to improved and overwhelming critical, ki critical, and increased multiplier; for these feats all natural weapons are treated as unarmed strikes. On the other hand, weapon focus (and the superior and epic versions), weapon specialization (and the epic version), and devastating critical make use of the type of natural weapon when determining if they apply.
As these slots are intended to represent natural weapons, most animals make use of these slots, but few humans and demi-humans do.