>>906244A mask is strapped on their face which allows them to breath in fresh air, but the exhaled air can only escape through a tube which is connected and sown into their asshole. There is a small vent that allows air to escape from the mask, but only enough to keep themselves in a perpetual state of suffocation.
As they try and pace their breath to keep their intestines from exploding, they eventually can't take it any more and inhale a big gulp of fresh air, but cannot hold their breath long to ven't all the air. As they forcefully push all the air out of their lungs, they feel their intestines start to rip and air starts trying to escape from under their skin. This continues until they pop.