Jeff hesitated before deciding whether he should do this. While he did want to try transforming into an animal, and the thought of becoming a random one was quite exciting, he wouldn't want anything bad to happen. As such, he set the change to only be for two hours, which he thought should be plenty to try out being an animal for a while. Concerned about becoming a fish and drowning or similar, he also set the machine to find him an appropriate setting for the duration of his change.
Satisfied that he had covered some basic safety precautions, Jeff gulped and activated the change. The machine immediately locked itself while it worked, and Jeff felt an electrical tingle shudder through him.
The first change he noticed was that his clothing was rapidly feeling far too tight. At first it was merely uncomfortable, but it rapidly started to hurt. With a great deal of effort, he managed to pull off his shirt, the fabric tearing as he tugged at it with newfound strength.
His jeans offered much more difficulty, and Jeff's fingers ripped holes in the fabric before he managed to free himself from them. By that time, his feet had grown so much that his socks gave way with a long, slow tearing sound. Shortly afterwards, his underwear followed suit, the waistband snapping as he outgrew the elastic.
Blushing as he was rendered naked, Jeff looked around to see that his eye level was now at the top of his door frame, and he was still growing. The room around him seemed to be rapidly shrinking, and with a loud creak, the chair he was sitting on gave way and snapped, making him land on the carpet with a heavy thud.
Struggling to right himself with a body that was feeling incredibly heavy and slow, Jeff felt his skin grow number and thicker, the color darkening from its natural hue to a stone like grey. Whorls and wrinkles like weathered stone began to creep across his roughening flesh, and beneath the grey hide he could feel his muscles swell and pulse with heat as he grew stronger and more muscular.
There was a creaking arising from Jeff's jaw, and he gradually began to see two points rising in his field of vision. He realized he could feel something thick and hard pushing out from the sides of his mouth, and raised a grey hand to feel that he now had tusks.
His nose twitched, the cartilage within shifting as it grew longer, flesh thickening and stretching as his nose began to grow into a trunk. The feeling was oddly satisfying, and Jeff found himself holding his growing, fleshy nose in both hands, stroking the rough skin as he began to massage his growing trunk.
Grinning with delight at his changes, Jeff began to twitch his ears, feeling them grow outwards into huge, thin grey flaps that waves either side of his head. He waved them experimentally, not noticing as his hair fell out to leave only thick grey hide.
With a small ache and odd wriggling sensation, Jeff's tailbone began to grow, lengthening into a flicking whiplike elephant tail. His whole body was growing wider and rounder, muscles and girth packing on at an astonishing rate.
The changes were quickly making Jeff grow aroused, and his cock was so far unaffected by his changes. Poking it with his hands, he grunted in annoyance as he found it difficult to grip. His hands and feet were growing wider and rounder, palms flattening as they became like grey tree trunks, transforming into the clumsy feet of an elephant.
Twisting his dexterous trunk down, Jeff grinned wider as he opened the mouthlike end of his new nose, closing it over his cock and slowly stroking himself off, his massive body shivering with pleasure. As he pleasured himself, however, his cock seemed to shrink, making it hard to grip in his trunk and frustrating his desires further.
Poking at his diminishing manhood, Jeff felt his trunk sink inwards strangely, pushing into a growing warm, wet crevice. The sudden arousal he felt at that was overpowering, and he began eagerly thrusting his trunk against this incredible new orifice, his body continuing to change as his posture altered to that of a quadruped.
Soon, his huge new four legged body was too large for him to continue his activity, and his trunk slipped out. Rolling over, desperate and horny, he struggled to his feet. Not yet realizing what had just happened, he watched as the room around him shimmered like a mirage, disappearing into nothing to reveal a vast, dusty Savannah.
Jeff looked around himself in awe, feeling the heat of the African sun pounding onto his hide, and the dusty ground beneath his feet. He could barely focus, however, with the incredible lust that was pounding between his legs. He raised his head and trumpeted loudly, expressing his neediness with the only form of speech he still possessed.
It was then that he realized that he was not alone. There was another elephant standing beside him, one that was oozing a potent, masculine aroma that made Jeff's knees shake weakly. The other elephant moved to Jeff's rear, nuzzling his flank affectionately.
Jeff considered running away, but something about the bull elephant made his surging desires grow more intense, and he found himself raising his tail instead. As the massive beast raised itself upward, pressing its titanic bulk down onto Jeff's back, he suddenly realized what was happening, and what had happened to "his" cock.
Before Jeff could do anything, she felt the bull elephant's massive, thick cock press against her pussy, his huge maleness slipping inside with a rush of orgasmic bliss that washed away Jeff's fears in an instant, replacing them with mindblowing pleasure.
For two hours, Jeff reveled in the incredible power of the bull as he pounded her tight virgin pussy, the new elephant's primal desires leaving no room for sentient human thought. Only when her mate finally unloaded a river of gushing, hot elephant cum into Jeff's womb, and her mind was blown with an electric orgasm, did she finally come to her senses.
It was also at that moment that Jeff heard a voice in her head.
"Time limit over. Attempting reversal."
There was a pause, Jeff still reeling from post-coital exhaustion.
"Reversal failed. Subject is pregnant. Reversal will be attempted after birth. Estimated time: two years. Enjoy your Chronivac experience."