obviously it's not a continuous stream. my curiosity is why
everyone has clean poops sometimes. you do it, it's out. you go to wipe.... and nothing on the paper. clean BM. if not, that means there's still poo. so the other x% of the time the sphincter just kind of cut it off. why?
I would assume it's due to the way the feces are transported throughout your small intestines and colon.
There's no constant pressure coming from your stomach, pushing the entire mass through the system, but rather via peristalsis
Your intestines clench up behind a piece of poop and relax in front, thereby moving the piece a bit forward.
That way, you get these compressed, discrete pieces instead of one long playdoh snake. (unless you have diarrhea or something. Can't really form 'balls' out of something that is entirely liquid.
whether or not you end up with a clean anus is all about the consistency of your poop, which is strongly related to your diet (how little / much you drink, how much fibre you consume).