A couple of weeks ago I was at home, waiting for an important phone call, when I got the urge to poop. I sat on the pot and began pooping. Of course, as the poop was emerging, the phone rang. Since the call would go to the answering machine on the fourth ring (and I definitely did not want that), I had to go and answer it.

As an experiment, I tried to stand up without squeezing off the poop that was hanging. However, the instant I started to get up, my anus tightened and dropped off the external portion of the poop, thus leaving me free to get the phone.

Upon thinking about it, I remember a couple of past times that a similar thing happened. Once, on a mall toilet, I was counting change for some reason when a quarter fell and started to roll; when I leaned way forward to pick it up, the turd that had been sliding out slowly suddenly shot out as my anus clamped shut.

My question is about this apparently automatic response to a sudden change of position: is it what I have heard referred to as the "anal wink"?

And if so, why do we have it? I would guess it has an evolutionary function, as it obviously is designed to cause a sudden poop drop when a more gradual one is in the process. Thanks for elucidating this phenomenon.