Jacob wasn't yet satisfied of messing with the transformation fields. Clicking on the next box, he typed in "snake" and noticed the sliders drop down to 33.33%, or one third of each field. Fearing he may lose his ability to use the computer if he became too animalistic, he changed human back to 50%, and set horse and snake to 25% each. Avoiding another error message, he left his mother at 50% horse, and his dad to 50% snake. He noticed a dice button when he clicked on his sister, and decided that he would click it once, and leave the percentages to the computer.
After he pressed enter, he changed again, with his skin toughening, and his nails stretched slightly into claws, and his tongue became forked, but still the same size and general shape as before.The most surprising snake came again from his genitals. He felt a strange force pulling it on both sides, and eventually it split into two identical horse cocks that slowly retreated into his sheath, and then his sheath pulled back into a new opening that looked like a vaginal slit, but housed both of his penises (now over a foot, maybe 1'3") inside. The only other major change was that his eyes became slitted, like a snake's.
Looking to his father on the computer, he was surprised to see a full naga, with scales running all the way up his body. He only wore a shirt with some old rock band logo on it. The only human parts left were his arms, still shaped normally, but with scales running down them as well, and his short, messy hair. He noticed that his dad had remained on omnivore, despite the drastic change
Jacob quickly realized where he went wrong. When he randomized his sister's attributes, she had ended up being 55% snake, 27% human, and 18% horse. since she was by a large majority snake, and her father having the only snake traits in the household, the computer had set his father to 80% snake, which he hadn't noticed because no error message had appeared. His sister was a more stable naga, with the upper half of a human, retaining her horse ears, her nails had become hoof-like similarly to Jacob, and fur only went up her hand to her wrist. Her tail was colored similarly to her father's, but bore a slightly more tannish hue. Her hips were wide to accommodate for her large tail, but the weird ting was that she had two tails, her horse tail appearing at the end of her snake body.
His room suddenly changed as well, to support a young horse/snake/teen. His carpet faded away, leaving a soft, even floor he wouldn't trip on with hooves, nor would he make much noise with his hooves clopping like they would on hard surfaces. His bed changed again, becoming wider and longer to support his larger frame. His chair now had a space to put his tail through, and his desk was a little larger, since his arms had also grown slightly. Thankfully, his computer had remained unchanged. Something weird though, was a shoebox-sized container marked XXXL, and upon closer inspection, it was filled with big condoms, large enough to cover both of his penises at the same time while still keeping everything inside.
Suddenly, he felt a strange heat spread over his body, and his penises grew fully erect, his sheath pushing out of his slit, and his heavy equine cocks growing and growing until they looked impossibly big at an astounding 1'6", much larger than Jacob had guessed from a minor species addition. Jacob reached out to his box of condoms, equipping one with a practiced stroke he didn't quite remember doing before, but he didn't care. He only worried about one thing right now, he needed to cum. He wrapped his hand around one and started masturbating. He began to feel uneven and wrapped his other cock with his other hand, sending waves and waves of pleasure from the movements of his arms. As this went on for several minutes, half an hour had suddenly gone by. "Damn this equine stamina" Jacob thought to himself as he finally sat down in his chair without a break from quickly rubbing the full length of his shafts. however, not long after, as he felt he would go crazy, he felt a wild churning in his large taut balls, and with the strength of a wine bottle's cork flying out at a party, Jacob began to send long ropes of cum deep into the condom. He quickly learned why he needed XXXL condoms, as this one filled at an impressive pace. When he finished, he had tied off his condom so it wouldn't spill on the floor, and saw it was about the size of his backpack. He left it in his trash bin and, with a slight grin on his face, turned back to his computer, the Extreme Reality software still on screen, ready for his next change.