Isaac could feel it, the thickness at the base swelling more and more, each time he thrust down. It caught at the rim of his hole, pulling him further open each time. The sounds that came from him were still technically human, but not enough to form words. Smalls barks, grunts, and eventually, howls, were pulled from him, spurred on by Derek's words.
Along with the pleasure of it all, Isaac was slowly starting to realize that there was another sensation as well. Derek's touches hadn't changed, but the wolfsbane had left Isaac weakened and struggling to heal. Bruises were forming over his hips, blossoming into place whenever Derek pulled him down. The edge of lingering pain made the pleasure sing even more, and Isaac chased after both feelings at once.