Board Thread:Speculation House/@comment-24994749-20140808215337/@comment-24994749-20141209013215

Animals have also been stated to have aura. Being semblance stated to be just the active form of aura, an animal should also be able to develop it. (In the dvd comentary they mention there is actually something special about Zwei, I'm going for it being him having received training to use his aura actively.)

So it's posible that part if the stigma against faunus comes from the Grimm being less agressive against them than they are towards humans. Maybe, like animals, Grimms don't feel particularly interested in attacking faunus unless the faunus in question faces against them.