Spike, for his part, was hornier than he had ever been. His new penis and balls desperately were desperately crying out for attention, his whole body felt flushed and hot, and he needed release. The almost ecstatic pleasure was almost agonizingly insufficient. His hips started quivering, practically humping into his own mouth, as his body almost mindlessly answered a primal need to mate. The base of his cock started swelling, which confused him greatly, but the strange round growth turned out to be the most sensitive part yet, and felt unspeakably luxurious to wipe his tongue against. Before he knew it, he was cumming, ejaculating longer than he ever had! In that moment, Spike didn't care that he was naked in front of everyone anyone else who might come along. He didn't care that he'd just brought himself in front of a climax in front of a woman whom he didn't even know. He only cared about the sensation of cumming: the relief, the weakness in his legs, the sense of release, the smell of sex, the comfort of his own tongue cleaning up the mess, the rhythm of semen spurting through his cock, the ... the swinging of his lower vertebrae?
When Spike finally started coming down from his self-induced sexual high, he tried to figure out what was slapping the sidewalk. He could feel skin and hair bouncing against the rocky surface, and he sensed vibrations pulsing through his backbone from each impact. Another wave of euphoria from his nether regions caused those feelings to increase in speed and intensity, which rattled his mind almost as much as the orgasm! He even felt a sort of strain back there, as though his own muscles were getting pushed to the limit ... somewhere.
Eventually, Spike happened to glance behind him and see a long black object flexing in and out of view from the other side of his torso. Bending around as far as he could (and Spike could bend pretty far now), he saw something long, thick and furry sticking out from the top of his own butt crack, and it was waving frantically, sliding across the ground and thumping against it. 'That can't be what I'm feeling, can it?' he thought, but as soon as pleasure and excitement were dethroned by confusion and focus, he saw it stop wagging and stick out straight. Even weirder, he actually felt himself automatically holding the thing still while he stared at it. Reaching out to touch it, he gasped to feel a hand against a strange new part of his body somewhere far behind his back.
"Wh-wh-what IS this?!" clutching frantically at something which was obviously his now. Most humans wouldn't have understood his words with that oversized tongue flopping around, but Jennifer could understand anything she wanted to understand.
"Man, you ARE a dumb one!" she said in a much less seductive tone of voice than before. "Can't you even recognize a dog tail?"
"That's not what this--I mean, this is MY t--I, I mean, whatever it is, it's attached to ME, and I'm obviously not a--"
"Did you honestly think I was going to leave you human after what you did?" she asked.
"Wh-what do you mean?" he stuttered, lurching awkwardly to his feet, new tail firmly perched between his legs.
"You know, what you did to Reese..." she commented. He only stared blankly at her. She rolled her eyes. "The one that Rad calls the red-headed bimbo. The one you went up to visit. The one you helped attack in my dorm room!"
"Oh," he said vacantly, seemingly at a loss for anything to say, staring intently at his tucked tail. As strong as the urge was to keep it shielded down between his knees, he knew it didn't belong on a person and he wanted to be rid of it. "You--you can make it go away?" he asked in his garbled half-changed voice.
"I can, but I won't. You seem to like dogs. You certainly didn't have any more self-control than a rutting animal when you came up to our dorm room earlier this evening. You wanna act like a dog in heat? I'm gonna let you be one."
A flapping feeling in his ears had already distracted him. He reached up and felt that they were longer and broader and more flexible. He felt a strange motion in them when he gulped and tucked his tail up tighter. He whimpered loudly.
"Ah, now you understand. You didn't think you were going to pay for what you did for Reese, what you did to other girls. But now you're paying with your humanity. No more weightlifting scholarship, no more sports buddies, no more parties with the frat, no more dirty jokes, no more opposable thumbs. No more clothes except that dumb spiked collar of yours."
Spike felt up to his neck where a familiar pressure was still wrapping him snugly, and sure enough the collar was still there. He wanted to rip it off. 'I'm not really gonna be a dog!' he thought, but his hands couldn't get a good grip. He looked down and saw his new front paws for the first time. He tried to move his thumbs, but they were numb.
"Look on the bright side, Spike," she said. "You get to go around naked, showing off that big dick of yours that you wanted every woman to see. You'll never have to worry about finding a toilet again. You won't have to worry about final exams any more. And you can reach just about anywhere with that big floppy tongue of yours." Surprisingly she actually saw his dick poke out again just a tad, and his tail even managed a very slight wag. But she continued: "On the other hand, you could always end up in a shelter somewhere, and if you ever attack a human again like you attacked my roommate, you will almost certainly be put under anesthesia ... permanently." His long tail drooped back down. When his long black fur finished growing and his muzzle was complete, standing in front of Jennifer was a large black pit bull. He sniffed the air a few times and that pink dick of his came out again. He didn't know he was smelling a female beagle in heat on the other side of town. Jennifer knew his human mind was no match for his instincts as he ran away into the night.