while sex was being had, someone accidentally pooped in a spurt of unbridled passion. Since the poop was had during sex, the emotions felt, the scents smelt, the sights seen and the textures touched during sex were then intrinsically intertwined with poop in that persons mind, resulting in an immediate erection/wetting whenever poop was had again. That is some power. And the birth of poop porn. Its circular logic. If the sex had can change a certain song being played, than it can also change a certain bodily function being made.