Bones can be applied to a group of objects (like deformers), that's why they deform the horns . So just parent them to the head bone and they shouldn't deform anymore . Later, you will have to set up skinning to avoid other strange deformations that may appear elsewhere on the model . And yes, you should set up more elaborate constraints to avoid the twisting problem . Also, manipulate the bones with care, they're very touchy ! I hope this helps, litst