Jeff was frustrated, to say the least. He had wanted to be the hero, not the hero's steed! Now instead of having adventures himself he would just be carrying around some guy to his adventures. Clearly, choosing a random change had been a mistake. He'd assumed that he would end up as a person, or at least whatever qualified as a person in this world of dwarves and elves and orcs, but clearly he had been mistaken, and a horse definitely didn't fit the bill. It was something different, to be sure, and maybe even something interesting, but it wasn't what he wanted! If he wanted to be an animal then he would have chosen to be an animal. He whickered in frustration, making the equine noise unintentionally, and tried to think of what to do.
But something strange happened. As much as he tried, Jeff couldn't think of a way out of his situation. In fact, thinking in general was harder. His brain was getting thicker, foggier, and the only thing he could think to do was to wait in his stall for his rider... wait, his rider? Oh no, the mental conditioning! He tried to shake it off by shaking his massive, elongated horse-head, but that only jumbled things up and confused him further. What was wrong? That he was a horse, of course, so he had to stay focused and find a way out... but why? What was wrong about being a horse? He WAS a horse. With that realization, things seemed to settle in his mind, and he felt a lot calmer, his frustration evaporating. He remembered being human, but he remembered being a horse too, suckling from his mare mother, running in the field as a colt, mounting mares, being trained under his rider. He no longer minded having a rider, it was his entire purpose to loyally carry his Rider around. He was his steed. Jeff... Jet knew that he was really a human boy from another world, but it didn't matter and he couldn't bring himself to care, since he was clearly a horse right now. He felt like a horse and thought like a horse--that is to say, not much. He didn't need to think, anyway, that was what he had a Rider for.
Jet stood and waited calmly in his stall, breathing in the rich scents around him that he didn't realize were much stronger than anything he could have smelled as a human. There wasn't much in his head, other than a vague sense of anticipation and eagerness to serve his Rider and carry him again.