The lack of more changes really disappointed him. Jason had been so excited by all this, he had hoped that it would be a complete change. His balls and sheath were still human pink, even. With nothing further happening, he was too tired to get off the horse to fuck it, but he was still horny, so he started to stroke himself, admiring the feel of his new dick and the medial ring and the bumps and grooves at the top. The horse kept on walking as he pumped himself and got closer to orgasm. He leaned back in the saddle and closed his eyes as he thoroughly enjoyed the masturbation session. He even developed a little flare as his cock tip ballooned slightly while he neared climax.
"Ohhh" cried Jason as he came with his horse cock for the first time. The spray of cum went straight and his such landed around the saddle and his legs, with some getting on his shirt. Tired from all the orgasm he had had that day, and the vernal day itself, he slumped forward in the saddle, satisfied but spent, and waited for the horse to finish taking them home.
The steady rocking of the mare’s familiar gait lulled Jason into a sleep. The next time he opened his eyes, he was still in the saddle and seated on the mare’s back. He snapped back to consciousness, sitting up and gripping the saddle horn. His eyes widened. It was dusk, and a light fog had begun to rise up from a nearby stream.
Jason gasped, realizing his total lack of pants, and for the first time the state of his transformed dick clicked in, the fog of arousal and sex clearing from his mind. In a state of confusion... and shame... Jason glanced around. This wasn’t home. In fact, he didn’t recognize where he was.
A whinny brought him out of his thoughts and he glanced down across the neck of the mare and saw her looking up at him. She had stopped completely, far from home. Jason stared warily. The mare stared back evenly, tilting her head to the side to glance at him. She huffed in defiance, tossed her mane, and stood fast.
“H-Hey!” Jason said nervously. He had a sick feeling in the pit of his stomach. He tried to get the horse moving. “This isn’t home at all! Come on, walk on! Walk on!”
The mare gave him a wicked smirk and shook her head in defiance.
“I said walk on!” Jason commanded, and then went white as a sheet as he realized what had just happened.
The horse let out a high pitched whinny of delight at his realization and shook with amusement, taking a few steps back. In a panic, Jason slid off the saddle, ass and sheath exposed below his faded denim shirt.
The mare purposely bumped him as he dismounted, almost sending him tumbling onto the ground.
The human turned, trembling a little, and he stared at the horse in slack jawed disbelief. He glanced down at his now sheathed cock and reality hit home. It was… reciprocal. He changed. She changed. In fact, they were now both infected with the transformation virus, but they both required a little something something to progress their conditions.
“Shit,” Jason whispered, staring at the mare in awe. “When…” he waved at the animal, too scared to say it.
The mare quickly pivoted on her hooves to face the man. Her eyes were light and excited and while she obviously couldn’t speak she was clearly intelligent now. He stared at the dried white in front of the saddle and gulped.
The mare swayed her tail excitedly and clopped forward on the grass, face to face with the man. She sniffed deeply of his face, which still smelt like her own sex, and closed her eyes, savoring her own scent mingled with that of her favorite human. She placed her head on Jason’s shoulder and sighed deeply.
Jason had gone pale and he felt sick. Shit. His wife, how would be explain… that? He now had a sheath and a bigger thicker (though small scale) horse cock. The mare he had fucked was now intelligent. Fuck, how would he explain that to Taylor?
The mare must have somehow sensed his growing fear and shame, because she stepped back and nudged his chest gently, as if to say it was okay.
“N-No… I… don’t know how to explain… what…”
The mare’s own eyes widened and she nodded gently in understanding. She considered something for a moment, head tilting, and with a sly look on her muzzle, she gently raised her right front leg and her elbow joint pressed into Jason’s groin.
The man gasped as the horse winked at him, turned to present her flank, and glanced back up him eagerly. Another part of her was winking as well.
“Oh God...” Jason gasped, as night began to fall on the meadow. “W-We can’t! I’ll... I’ll...”
The mare neighed insistently and stamped her back leg in annoyance – come on, man, fuck me!
Jason glanced down, surprised as his length of cock slipped from his sheath and began to grow erect again. He glanced up, seeing the mare staring at him expectantly with almost pleading eyes, and her inflection was clear. Please, please, take us further!
With a dawning realization Jason stepped forward with a gently bobbing erection of his new horse dick and touched the mare’s ass. She swooned and nodded, the touch making her visibly wetter and excited, a single bead of her juices dripping from her slit and down onto the grass.
He was now responsible, however insane it seemed, for giving this horse the gift of intelligence. He felt a strange curiosity and desire course through him. How... far could they both go? Would be become more horse? Would she become more human? What would happen?