Mike woke, his arms still around the boy's chest. It was obviously still night, but there was enough moonlight filtering through the windows of the barn to see. His nostrils flared slightly, drawing in a curious mix of equine and human scents. The first realization was that his nostrils had flared. He reached up and felt a protruding face, not a muzzle yet, but graced with thick, pliable lips and soft nostrils that he could move. His sexual release had taken him a step back towards being a horse. Curiously, he did not mind that at all, despite his pleas to Tye to make him a centaur again.
The second realization was that the boy was no longer quite human. His skin was covered with a fine layer of pale hair, and his ears were pointed and higher on his head. It was also pretty obvious that the boy's sexual equipment had altered, now much larger and darker, "The magic is working." Mike spoke softly, but the boy came awake instantly. "Huh? What?"
Mike kissed the top of the boy's head. "I said the magic is working. You are part horse."
"Oh!" The boy scrambled up, staring at his arms and body in the darkness, then feeling his face. "Yeah! I can feel it!" He turned to face Mike. "You too! Your face, it's really horsey!"
Mike shifted and rose to all fours, shaking off the straw. He felt good, but not quite right. Being a Shire had become so natural that this centaur body was now what felt off. "Not horsey enough."
The boy grinned. "Me neither. I can fix that for both of us, but remember that it will also change how you think, at least a little.
Mike considered that. "Well, we'll know more once you masturbate me again, and we see how much more that changes things."
Needing no further invitation, the boy moved beside Mike and then stooped to reach under the centaur's belly. Cool hands caressed his sheath, and then the shaft than quickly emerged. Mike found himself getting quickly aroused by the combined thoughts of him and the boy both changing. The massive Shire stallion he had been beckoned, and the image seemed to take on a physical presence that drifted into his swollen testicles. He grunted as the boy brought him closer to orgasm, feeling pressure build. "This one is going to be big and messy."
The boy moved under Mike, making sure that none of the expected spunk would be wasted. "More cum is more change."
Mike grunted again, then remembered what the boy had said earlier about control. "We are powerful stallions. Young, perfectly matched Shires, bonded together as brothers and lovers, identical in every way."