system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:You know when you have to poop really bad and are trying to hold it in and then you get that kind of bubbly feeling in your bowels and don't have to go as bad anymore? What has physically changed that relieved some pressure?
gpt
Contraction of bowel into the anal canal is peristaltic meaning it comes in waves. The first anal sphincter is involuntary so when you need to go it relaxes letting poo to the canal. Then you tense your voluntary one. When the peristaltic wave passes you mo longer feel the urge even though the canal itself is full.