when we die, our brains no longer send these messages to our muscles. During rigor mortis your muscles seize up tight, but after several days they relax. The good ship decomposition has set sail, and all muscles relax at that point, including the ones that keep poop (and pee, for that matter) inside. So, if you happen to have feces or urine in the chamber at the moment of your passing, they’re now free to go.
