As pleasurable as it seemed now, Derrick did not want to spend the whole two weeks of his vacation being the personal slave to a centaur. And he had a bigger concern that the job was not just for two weeks. Mustering up all the willpower he could manage, Derrick stepped back and away from the centaur. "I... I not... am not.." He had to struggle for the words and was afraid it might already be too late. The reflection showed him to be almost fully changed into one of the horse-boys, though his skull was not quite so flat, and his features were still vaguely recognizable. Still, his mind was clearing now that the centaur's hand was not reshaping his skull. "I do...not.. want... to... stay.. here."
There was disappointment in the centaur's eyes, but he smiled and nodded. "There is time yet. You accepted the change - I could not have made it otherwise. If you change your mind, you are welcome back any time. You will always know the way to my stall."
God, the centaur was beautiful and amazing and Derrick felt a powerful urge to surrender to him now, but resisted with great effort. As he did, the horse-boy in the mirror shifted and became more human. Derrick's mind cleared more, and he moved fully out of the stall. Some of the changes had reversed, but when he looked down at himself he was still far more like the stable boys than his old human self. That included the massive, dark sexual equipment - somewhere along the way he had lost his clothing - and the odd, three-fingered hands. He walked on hooves now, and the odd elongation of his arms and legs made him better suited to caring for the massive centaurs. He also understood without being told that he was somewhere near the dividing line between beast and human, though he was not sure which side he was on.
When the centaur see the sad face of Derrick he was sad too.
“Hmm. I couldn’t change you back to normal and I know you wouldn’t like to be a Stable boy. But I can offer you another option.” Derrick was suspicious, but when he saw the centaur's face, he nodded in agreement.
The centaur walked arround the boy and then pressed one hand against derricks back, so that he was forced to forward and stood on all fours. With his hove like ands and long arms it was easy to stay in this position. With the other hand the centaur reached between derricks legs, forced him to spread his legs. The centaur start to masssage derricks balls and cock. He feels that his skull become full human again, only his ears are still horse like. On the other side he feels that his butt cheeks would open and presents his new horse anus. Derrick don’t know if it is the right way he would like to change but the sexual stimulation and the new horse hormones feels so good.
When he looks to his hands he saw they are full human again and his arms also full human. But this have his prize. His legs, feets and his but are growing into a full horse form. While the rest of his upper body become full human the last change of his lower body. His deformed genitals are become that of a horse. And he shoot his first horse seamen out of his new horse cock.
The centaur took his hand from the back of derrick. And allowed him to stand up back to his new legs. Derrick was shocked and fascinated at the same time. He is still a freak. But his mind is human and he love what he see. The centaur smile as he notes that the former humen are very proud to show his new body.