The Russian scientist Ivan Pavlov famously experimented with the "conditioned reflex" -- that is, conditioning a subject (in his case, a dog) to associate a particular reflex, such as salivating, with an unrelated stimulus, such as ringing a bell. He noticed a natural reflex in dogs that would make them salivate when they smelled food. He started ringing a bell every time he presented food until the dog associated the bell with the smell of food. From then on, he could cause the dog to salivate simply by ringing a bell, even with no food present: a conditioned reflex.
The conditioned reflex is present in humans, it seems. In our butts. Our natural reflex is to feel the urge to poop when certain digestive parameters are met. But some of us feel the urge to poop for other reasons.
For example: In college, I used to work for the online magazine. I'd go about my day but eventually end up in the magazine office, sometimes at 2:00, sometimes at 3:00. No matter what time I arrived, and no matter what I had eaten during the day, however, my arrival in that office would bring with it a sudden and intense urge to drop a deuce. That office triggered a Pavlovian response -- a conditioned reflex (the need to poop) from an unrelated stimulus (walking into an office).
The idea of Pavlov's anus was first brought up by Poopypants almost two years ago. I've been meaning to revisit this subject ever since. When we first discussed it on the forums, people said "coffee" or "cigarettes." Those aren't Pavlovian, because those substances physically stimulate the bowels -- coffee, for instance, is a diuretic. That's a physical stimulation of the bowels. It's not Pavlovian. The magazine office's effect on my pooper *is* Pavlovian because there was no physiological interaction between it and my bowels. It was purely a conditioned response.
So tell us: have you experienced Pavlov's anus?