Peristalsis

Peristalsis should play no direct role. Of course, peristaltic movements are the contractions of the GI tract from the stomach to the rectum where periodically, ring like squeezing contractions of the intestine, which is for the most part shaped like a tube, push the contents distally. These are involuntary contractions and you don't feel them unless for some reason you have intestinal cramps in your small bowel or in the case of your colon you feel a large peristaltic contraction of the lower approximately 3 feet of colon, upon which you can generally know you better start heading to the toilet because a full rectum that needs to be urgently emptied is the next thing you're gonna feel.

But as far as the rectum goes itself, when it is empty it is relaxed and not contracting and even when you're relaxed with an Aneros in, the rectum is not necessarily trying to push it out with peristaltic contractions. Instead, what you try to get to happen is that involuntary contraction where your anus, without you contracting it yourself, sucks in the Aneros and pushes and rubs it against the nerves going to your penis that cross right over the back of your prostate resulting in an orgasm, just unaccompanied by ejaculation.

That's why this orgasm lasts so long and doesn't result in a refractory period.