Inexplicable Phenomena

In my sessions I usually lie on my back with my knees bent. Now I noticed that when I switch to doggy position for about a minute & then go back to my usual position, I instantly get very fast sphincter contractions...I think it's 3-4 per second...It's like some kind of alien force is hammering against my prostate...

I don't know why this is & what's happening in my body when I do this, but it seems to work very reliably, at least with my Helix Trident. Didn't try it with my MGX yet.

Now I wonder if it's just me or if it's a general thing that could work for everyone with a butt & a prostate.
Maybe there are other position changes, exercises, whatever things to do that trigger similar inexplicable effects?