That used to happen to me when I was a kid and was sick, and took a Sucrets (I think that's what it was called). What kind of bullshit medicine will suppress your ability to cough, but not the need?
Maybe we're lost in the desert/jungle/tundra/whatever and are starving.
Or maybe back in the caveman days, some people would just be curious.
Also, would the anus really be seen as so gross if nothing about it smelled bad?