Derrick thought about that. "Thinking like a horse would be really different. But you'll change me back, right?"
Hephaustus shrugged. "As much as I can. But I doubt you will want to return to being a centaur."
If Derrick had not been feelin so aroused he might have paid more attention to the reply, but he was already fully erect and the mare's scent was calling to him. "OK! I'm ready."
Placing his hands on the huge centaur's chest, Hephaustus concentrated and began to rub the coal-black skin. Derrick felt more of the strange pulling, this time watching in awe as his muscular arms dwindled and shrank into his chest, which was also changing shape. Then Hephaustus moved his hands up to Derrick's face, tracing the edges of his jaw and nose. Both began to push outward, forming a huge mass that split his vision. Already equine in size and function, his eyes drifted apart to the sides, while his ears moved up tot eh top of his now-flattened skull.
The transformation was not at all painful - in fact, Derrick felt both pleasure and a curious sense of being restored to what he should be. As the last traces of his centaur form faded away, Derrick turned his fully-equine head to stare at the magnificent Shire stallion reflected back from the pool. Although the centaur form had been of equal size, there was a purity of form and function in the horse that pleased him even more.
Hephaustus grinned and reached up to stroke Derrick's broad forehead. "The form is done. Now for the most important part. That which makes you truly a Shire stallion." His fingers pressed hard, send a wave of warmth that flowed deep into the former boy's skull. Derrick was puzzled, already fully a stallion. Hephaustus explained "Your mind and soul are being reshaped to match your magnificent new body. Your existence will be far simpler, more focused, with instincts and equine memories to follow instead of irrelevant human thoughts."
The warmth drifted through Derrick's brain, and he had the oddest sensation of things melting away like ice cream in the hot sun. It took a minute before he realized important things were fading - all of his classroom knowledge like math and science was leaving in a kind of mental regression. Middle school subjects erased themselves, then elementary school classes. It made sense, for a horse did not need those things. Derrick was more interested in new thoughts and memories - training under saddle, pulling plows and wagons, mounting many mares. Now even the knowledge of words and numbers faded away, replaced by equine body language and sounds. The warmth increased now, almost too hot in his head. Hephaustus concentrated. "The last of your human links - your soulfire. Accept the spirit of a horse, let go of your humanity forever."
Derrick no longer understood the sounds Hephaustus made, but he still knew what was happening and what was being asked. If the mare had not been so close, and his need so great, he still might have resisted. But the stallion's instincts and needs, his stallion's body, all screamed to forget all but the rich sweet scent of the mare. He willingly opened himself up, allowing the core of his very being to be reshaped, simplified, distilled. For a brief moment, Derrick realized that his place in the universe had just been irrevocably changed - no matter what form he might have in the future, he was now and forever a horse. And then the Shire stallion snorted and pulled away from Hephaustus, intent on the mare. It felt total satisfaction, complete sense of purpose, that only a beast can experience.
Hephaustus stood back and watched the animals mate. His hands glowed with a writhing blue-green light - the humanity of Derrick's original soul. Once willingly rejected, it could not be restored. However, soulfire was incredibly potent. Closing his eyes, Hephaustus drew the energy in, adding it to his already powerful core of magic. As it was absorbed, the soulfire lost definition, merging into the whole until it was nothing more than new power to reshape others.