Natural Weapons are inherent weaponry to the physical features of the creature possessing it – they require no explicit proficiency to use. The specific of damage and other effects is totally dependent on the specific physiology of the creature.
All natural weapons have the “natural” property – so easy to use they gain +2 penalty to use and familiarity (though not any skill necessarily) – it is part of who they are.Natural weapons cannot be used to parry or block unless specifically noted (usually meaning they defend with some armored limb or feature).
Humanoids: The basics are Kick, Fist, and Head-Butt. Many humanoid races have adopted forms of martial arts based on natural weaponry, adapting knees, elbows, and other parts and surfaces of their body for effective use.