When one has to poop, the feeling (initially) doesn’t come and stay. Rather, it comes, stays for a while, then goes away…then it comes back stronger, stays, then goes again. Eventually it seems to stay permanently, but not initially. It’s not just I this happens to, others I know have wondered the same thing.
So, why does such a thing happen? Why does it come and go and not just stay?
This thread from 2007 asks much the same question without much satisfaction.
I thought WhyNot’s post #5 answers it in full.
Not only does it come and go, but your sphincter muscles are somehow aware of precisely how long it takes to get home, into the bathroom, pants off and ***just ***make in onto the toilet.
I don’t know about anyone else, but I consciously suck it back in. It seems to me that the feeling of needing to poop is based on being so full that it pushes against whatever’s holding it in. If you can rearrange it where it takes up less space, then it no longer feels like it needs to come out.
As for feeling like you need to poop again after you are in the bathroom–that’s probably like the peeing thing. Your involuntary muscles release because they know you’re about to go, and so you’re consciously having to hold it in. It wouldn’t surprise me if the involuntary muscles are actually preparing so it will be easier for the voluntary muscles to get it out.
Me too.
TMI Alert!!! (but if that bothers you, you shouldn’t’ve entered this thread to begin with!)
The problem with this procedure is that if it happens too many times, it will have turned to mush, and instead of plopping out, it will splash out.
In my experience, the evacuation seems to be triggered by having some reading material to hand. Even the ingredients list on a bottle of shampoo will do, at a pinch.
To add a bit to WhyNots answer, the reason it comes and fades, and then recurs (repeat as needed) is that Peristaltic waves move in a one way direction down the digestive tract. The waves push the intestinal/colonic contents toward the posterior opening. These waves are not conscious, but occur at regular intervals day and night. Often the cycle occurs in the 10 to 20 minute time frame, but not always.
The urge to poop comes when fecal material enters the rectum and approaches the internal anal sphincter. The internal sphincter opens, and then the external opens. When we are potty trained, we can resist opening the external sphincter, and wait for the next urge to void the bowels. Babies can’t control the external yet, therefore more frequent and usually softer poop.
One of the dangers of putting off pooping in adults is that the colon is a very good organ for the reabsorbtion of water…so the longer one puts off pooping, the more water is removed from the fecal mass…the result is dry, hard and smaller feces; in fact they may become little hard spherical masses and in extreme cases must be removed manually.
Can you tell I used to teach Anatomy? Poop as soon as possible folks! Avoid constipation and possibly hemorrhoids!
Hey, I do that too! 
Damn, internet does it again. Where would I be without it? On the loo reading the words “Sodium Laurel Sulfate” thinking, “Am I being silly again?” probably.
<snicker>
I don’t know if this is what you mean, but I find that if I go when I first feel the urge, it’s usually a “one-wiper”. However, if I hold it and go later, much more wiping is needed.