”…Octavia no longer had to imagine what the pressure in that tank could do to a pony’s body; instead, she found herself imagining how she could possibly avoid complete embarrassment at Vinyl’s party. Passing for normal was a long-gone dream, slipping further from reach with each new cubic inch of helium pumped into her. Everypony was going to notice her new size; Octavia was going to spend the party apologizing profusely for accidentally bumping guests with her huge new belly and ponderous rump. And if anypony were to ask, she couldn’t even pass off her new girth as overeating: she was too light, too perfectly round to be anything but a gas-filled balloon. Octavia would have to admit there’d been an accident with a helium tank, and simply omit a few details leading up to said accident. And that was the best-case scenario; if she didn’t dislodge the helium tank soon…

Octavia shook her head, dismissing that chain of thought. She was going to free herself! And then finish the party preparations afterwards! She was still in control.

And then the lowest edge of her belly brushed against the floor, the sensation jolting Octavia back to reality. Her stomach was still swelling larger, and her rear wasn’t far behind. Realizing that further attempts to kick away the helium tank would be a fool’s errand, Octavia instead extended her foreleg back that direction. Twisting to reach back, she pressed her shoulder into the top of her inflated stomach, while her cannon squeezed against her puffed-out haunch. As she squished into the grey softness of her own inflating body, her hooftip brushed against the helium tank’s side—almost enough to get a grip, but not quite. All the while, she jiggled and shook at the slightest movement: her thick, bulbous rump cheeks slapping together, and her huge stomach fully resting on the floor. Octavia gritted her teeth and strained to reach back farther, squeezing inches deeper into her belly and backside—while they squished back with ever more pressure, bulging further around her leg as they filled with more and more gas. As her hoof crept closer and closer to a proper grip on that metal cylinder, her belly also crept across the floor inch by inch, spreading to the sides and pushing her legs further apart now that there was no more room to expand downwards.”

Only going to get bigger from here~ Read ahead if you like!