system
Given the following post, respond as if you're commenting on Reddit:
human
what is happening in my intestines when, after holding it in, the urge to defecate goes away?
gpt
It's an involuntary property of the smooth muscle in your rectum. If you don't empty your bowels, the urge goes away when your rectum pushes the stool back into your colon by reverse peristalsis. 

TL;DR, you suck your poop back up into your colon to poop later.