Finally she uncorked a vial and took a small sip of the centaur potion.
"Mmm," she murmered, "Kinda grassy, and earthy, like mushrooms or something..." Mary tipped the vial up and drained the rest.
Placing the vial back in the box, she had barely turned to the mirror when a wave of goosebumps raced over her entire body. Feeling a cramping in her feet, she glanced down and watched with glee as her outer toes began to shrink while her middle toes thickened. The nails expanded, wrapping around the growing digits and hardening.
Mary squealed and grinned. "Hooves! Oh, man! Wow!" she continued to stare at her changing feet as her heels lifted off the floor, her arches lengthening until she was forced to grip the wall and shift to stand on her tip-toes, now hooves.
Her skin above the hooves began tingling, and she was delighted to see fine white hairs pushing out and following the changes up her legs. As they reached her thighs, she expected to watch them thicken and fill out to muscular horse-proportions, and was a little puzzled when they remained relatively slender under the coating of fur. An ache in her backside distracted her though, and she twisted around to try to watch her tail grow out. Grinning, she reached back to rub the base of her spine, and could feel a small nub pulsing under her fingers. Suddenly her buttocks pulsed as well, gaining mass rapidly and pushing out along with the start of her tail.
Mary's mouth dropped open as she watched her spine continue to lengthen, her backside pushing out and expanding as an entire new torso began to form behind her hips. Her pelvis shifted, her joints flattening and opening up to allow a new ribcage to form behind them. Two more tiny appendages appeared on either side of her growing tail, and Mary suddenly lost her balance, tipping backward to land on her expanding rear-end. The new growths quickly filled out into two thick horse-thighs, the limbs lengthening as hooves formed to match her front legs. With her human torso still upright, Mary was astounded to feel the rough carpet beneath her lower body, rubbing along her second belly as she shifted to curl her hind-legs beside her
Something twitched at the end of her rump, and she was delighted to see that her tail had fully formed, long golden hairs covering the length of it and wrapping around her hindquarters.