He is led to his hotel room, feeling drained after the surgery. He undresses wanting no more than a hot shower and a good nights sleep. He walks into the bathroom still feeling a bit odd but then he looks down at the furry balls and dismisses the feeling, attributing it to the surgery.
The young man scratches idly at his back not noticing the new hairs pushing their way out of his skin nor the small nub forming at the base of his spine. He turns on the shower, and stands waiting for the water to warm up. "Who would have thought they could attach a dogs testicles to a human." He thought as he cupped them experimentally. It was then that his noticed his dick looked odd. In the past few minutes it seemed to have gotten redder. As he inspected it for more oddities he watched as the base swelled and his cock became painfully erect. It felt as if someone had inserted a rod into the base.
He watches in horror as the tip grows into a point and then disappeared quickly into a newly formed sheath. He stands in shocked silence starring at it until an odd poping sound makes him turn about. The small nub has grown significantly and now the man is left holding a long hairless tail. He tugs at it but the pain confirms that it is indeed his. The truth of what the surgery had done to him now stars him in the face. He is becoming a dog.