Luke squatted slightly and peed, and dropped her head. She was not really doing it on purpose - something in her dog brain told her to do those things. And the boy - the adult male Great Dane, was definitely responding. He sniffed and licked at Luke's opening, making her shiver and whine. He pressed against her and then started thrusting, his rigid pink cock hitting her rump and anus and thighs. And then he scored a direct hit.
Luke yelped as the big male drove into her, pushing deeper as he thrust, working his way over her back. The sensations were intense, both pleasure and need filling her mind. The Great Dane mounting her began to get more serious, gripping and humping with more purpose, driven by instincts more than curiosity now. Luke felt the Dane's knot swell out, locking them together as he jetted his seed into her. They yelp and whined together, until the male was finally spent. They still could not pull apart.
Luke struggled to clear her head, almost overwhelmed by the bitch's instincts and the powerful mating drives. It was a real battle, and when she twisted her head to look back at the Great Dane, she realized the boy was losing to the dog. His eyes were wide and confused, though he did not look scared. More puzzled, as if he could not quite understand what was going on.
Luke saw the boy's eyes change, the bright awareness that had been there before flicker and fade, until they were the eyes of a satisfied, happy, and normal Great Dane.
The clerk came in before they had uncoupled and groaned. "Oh, crap! I can't believe you guys screwed! One of you was a little kid! And now I don;t know if either of you will change back. Sex is a pretty powerful lock, and so is pregnancy."
Luke whined. he did not want to be stuck as a dog forever! But he could feel the dog's throughts drifting over his human ones.