John thought for a moment, he didn't like the idea of putting his mouth on this thing... Suddenly, he had a brilliant idea! Or at least, he thought it was. He twisted and wiggled a bit, reaching behind as he placed the hose on his back square between his shoulder blades.
"Perfect! So, now what happens?" John asked the vendor, and with a smile and a wink he turned the nozzle on the tank. The telltale hiss of the gas made John shiver, as he wondered what might happen next. To his surprise, he didn't notice anything immediately. Perhaps the vendor knew how nervous he was, and was simply going slow for his sake? "Carrie, I-" John caught himself mid sentence as he heard his own voice: it sounded... Higher? He only had a moment to think about what was happening to his voice, when he looked down at the rest of his body. His arms were starting to inflate, becoming harder to bend and move, along with his legs... Feet... Body... Everything! Even his neck and head were tough to move, and soon it was impossible for him to keep looking at his own body! Even worse, since his face had swollen, he found he couldn't speak anymore!
However, Carrie could see all the changes still! As he grew a bit rounder and larger, he even began to float a bit off the ground! But then, Carrie noticed something a bit odd about John. His face seemed... Softer? Maybe it was just the way he was stretched, but his face had taken on a very feminine look! And even though his whole body was ballooning out, something about it seemed less masculine... Carrie grew a little worried, but dismissed her fears as just an illusion, when she saw two unmistakable orbs appearing on John's chest!
"Ack! John! Y-You're...!" Carrie started to panic, it was clear what was happening to John now: 'he' was becoming a 'she'!