Kendra knew track tryouts were coming up, and wanted desperately to beat Antonia to the top spot. Turning to the still-running Chronivac, she entered "I am the fastest girl in school."
Suddenly, she found herself standing upright with her side facing the desktop, her athletic shorts and panties having spontaneously vanished, only to reappear on the far side of her room. She tried to move to get them, only to find herself firmly rooted in place, clad only in her athletics shirt and sports bra.
"What kind of program is this?" she said while trying to move her legs.
The reason for her predicament came soon enough: though she felt no pain, she could clearly see and feel her legs thickening, becoming so thick she couldn't bend her knees, even if she wanted to. More, she could feel her spine slowly pushing and extending backwards, her stomach starting to stretch under her as her vagina slid out of view. A deep groove appeared on her legs, running down both the inner and outer sides as it slowly deepened into a fissure. Her legs split, amoeba-like, forming two complete sets of human legs. The doubled legs were pushed apart as a torso, some three feet in length and just as lean and athletic as hers, slowly grew in between them, her lungs doubling in size and joining her heart in filling her upper torso, while a second heart joined the rest of her internal organs as they grew down into the lower torso.
When the changes were finished, the program released her from its grip. Her mind was at first awash with sensations once communication with her legs was reestablished - she could barely handle twenty little toes firing back the feeling of the carpet beneath them. One by one, she lifted each foot, wiggling and stretching them as she went. Her breathing was ragged as the dry air caressed her now-exposed rearward-facing vagina, the sensation of such pleasure so far behind her proving quite disorienting. She probably would have fallen to the floor, were it not for the extra stability created by her four legs.
She didn't need a mirror to tell her what she already realized: she had the look and feel of a centaur from Greek myth, but, besides her elf-like ears, she was still all human. She just happened to now be a human with four legs - a humantaur!
Kendra started to cry, mortified by her new appearance - she was now a freak! There was, in her mind, no way that the track team - or any team, for that matter - would even remotely contemplate the idea of even having her try out, let alone actually compete. And yet, she couldn't help but find something alluring - even exotic - about having four long, sleek human legs instead of those of some animal. Either way, she'd have to quickly adapt to her new body - at least until she could get her normal one back, if that was at all possible.
She began to slowly walk over to her athletic shorts and panties, still uneasy in her new form. Using a bit of leverage to work them up her rear legs, she managed to get herself dressed, though her front legs, completely void of any genitalia as they were, still remained naked. She then practiced getting around on her four legs, became adept at walking in under half an hour. In the end, she found having four legs to be quite comfortable, as she didn't become nearly as tired on her feet as she used to.
She even found her lower back to be very flexible, as she could still sit in a normal chair, the curve where her butt used to be fitting into the seat of the chair - the only difference being that when she sat down, she now had four legs in front of her instead of just two. So she settled on the practice of sitting on the floor, her rear legs seated Indian-style on the carpet while she used her lower torso and front legs as a tripod.
Seating herself down in front of her computer after closing and locking her bedroom door, she decided to study the Chronivac - primarily to see if her "condition" could be reversed, but also to see just what all she could change. Scouring through the program proved quite the eye-opener for her - she was dumbstruck by all the options there were. Fortunately for her, she found the option to preview changes and wisely chose to enable it.
As she was sifting through the options before her, she began to wonder "If this is what it's like to have two pairs of legs, I wonder what it would be like to have..."