Here, we will make the dwarf nod his head, regardless of what else he is doing. In other words, we will mix the nod animation with all other animations that he does such that the nod animation affects only his head.
AnimationController nod; nod = new AnimationController(this, dwarfAnimator.Animations["nodHead"]);
    // Add this to the end of the update method
    BonePose head = dwarfAnimator.BonePoses["head"];
    head.CurrentController = nod;
    head.CurrentBlendController = null;