The Spell Storing magical property for a weapon says
Anytime the weapon strikes a creature and the creature takes damage from it, the weapon can immediately cast the spell on that creature as a free action if the wielder desires.
If this property is placed on an Amulet of Might Fists, would an animal companion, with an intelligence of 2, be able to cast the spell stored in the amulet after a natural attack? Could it be pushed or trained to do so? This seems difficult, since handling or pushing an animal causes the animal to act on its next action. I'm not sure you can tell it to attack and use the stored spell.