The sentence on the TMS app's screen now read "The transman is currently the same sex as the centaur before had," though David wasn't quite sure if that would do what they intended, so they readied their fingers to undo if it something went wrong. They'd meant that as in 'had been'.
Taking a breath, the centaur hit Submit and looked up at their friend on the armrest of the centaur-approved couch. In the next instance, Alex's pants burst open, ripping the button from the waist of their blue jeans as a comparatively giant feral sheath was just suddenly there. Indeed, there was now a black-furred, equine-shaped dick covering jutting out from where Alex's womanhood had been an instant before. Testes that were easily three-inch round ovoids were covered in matted black fur, with dark-colored skin encircling Alex's hidden penis within the sheath overtop of them.
"Horse-cock!" Alex chuckled, unthinkingly putting her hands around them. "I love it!" he laughed. "I mean... these could be bigger," he grinned, cupping his balls, "But I love it!"
David glanced down at the app, which said 'Alex sports average centaur testicles'. Chuckling, David smirked and swiped to uncheck Alex's awareness, moving their cursor before the word average and adding above to right before it. Sure enough, when they looked up, Alaex's balls were now about four-inch round.
"I dunno... they seem kind'a big to me," David grinned.
"Nah," Alex waved one hand, unaware they were holding larger balls with their other hand still. "I have a threshold for how big is too big," he grinned, "And it's bigger than this...!"
Glancing down at their phone, David brought up the old sentence with a tap and deleted the word above, hit Submit, and then changed the lone word average to large... but when they glanced up at Alex, they still seemed unimpressed.
Maybe because Alex already thought they could be bigger, reality isn't changing that. No matter how big they are, they could always be larger, David considered. Flicking back on Alex's awareness, David actively held his phone while looking at Alex and altered large so that the sentence now read 'Alex sports gigantic centaur testicles.'
Alex gasped, putting both hands on their now seven-inch wide, ovid-shaped balls. "Oh, yeah. I love them!" he said, getting excited... not seeming to care as they could feel the mostly concealed penis inside it's sheath slowly growing harder inside their body. Since they were still mostly human, their organs had to somewhat shift out of the way to allow his length to exist... but now it was beginning to peak out from his sheath.
"Wait a second," Alex blinked, putting a hand up under their remedial ring at the top of their shaft. "Is this... your penis?" he asked, running one hand underneath the extending, widening shaft.
"I thought someone should make use of it," David shrugged. "I figured it made sense if we were going opposite sexes that swapping might not be bad."
"I love it!" Alex repeated. "But, you know... I said before it was average—"
"Love it, but want bigger?" David asked. Alex nodded their head up and down with great vigor. "Alright," David said, keeping Alex's awareness on this time. Hitting Refresh a few times, David found the sentence 'Alex's new cock was seventeen inches long when hard'. Again, David didn't know if that was big or not for a horse, but envisioning it did make her nethers wet again. Taking a breath, David swapped the written word seventeenth for twenty-four, adding more than half a foot to his length.
"Oh baby!" Alex said, making himself the first person who'd ever seemed ready to masterbate in front of David. He was now running a hand up and down his shaft while holding the base with his other hand.
Taking the scene in, David wasn't sure if they should say something... or what even to say. Beyond whatever gender their mind would decide on, there was certainly something enticing about the oversized mustang shaft before them. Taking a breath to try and calm themselves, when they opened their mouth to speak, what they said was: