Natural weapons are weapons that are physically a part of a creature. A creature making a melee attack with a natural weapon is considered armed and does not provoke attacks of opportunity. Likewise, it threatens any space it can reach. Unless otherwise noted, a natural weapon threatens a critical hit on a natural attack roll of 20. When a creature has more than one natural weapon, one of them (or sometimes a pair or set of them) is the primary weapon. All the creature's remaining natural weapons are secondary.