It all started for you when the reports on people getting attacked by wolves came in.
You didn't think much of it, everyone who had made it out of it had survived and didn't seem to have contracted rabies. They were freak accidents as far as you were concerned, at least until your girlfriend Katherine came back from a hike in the woods with claw and bite marks.
She told you about the creature that attacked her, it looked like a wolf but it also looked bipedal. It had run at her on two legs and gotten her good, she had barely made it out of there. It made her uncomfortable to think about it, but you were just glad she was going to be okay and you both tried to move on from it.
But from then on things got weirder. Katherine was a professed vegetarian but she suddenly started eating meat, first well cooked and then getting rarer and rarer. The sex between the two of you got more aggressive too, with her becoming more dominant and practically jumped on you when you got home as she didn't even bother to wear clothes around the house anymore. You didn't really care too much, it was strange behavior sure but you figured she was just letting her kinky side show.
Weirder still was the fact that your dog was starting to act weird around her. He seemed to get more affectionate when she was close, sometimes even sticking his muzzle up against her pussy and trying to get at it. You were embarrassed, but your girlfriend just laughed it off as if it was nothing.
Today was an ordinary day, you had gotten home. You heard the sound of your girlfriend moaning from the bedroom you shared with her. You smiled a little, she must've gotten started without you and was waiting for you to arrive so you stripped off your clothes as your cock started to get hard in anticipation.
However when you reached the bedroom you were surprised to find...