I looked up en.wikipedia.org/wiki/Anal_fistula - apparently it starts with an anal gland getting clogged. I've had that much happen a couple of times ... eat shelled peanuts, get careless, scrape a bit of peanut shell over my asshole while wiping, voila, I have a little lump inside. But what I always ended up doing was getting in the shower and compulsively squeezing the lump until it seemed to empty out (sometimes took a few tries). After that it usually refilled but was easier to squeeze the next time until it stopped being trouble. Whatever happened, still one asshole last I checked, so maybe that's a winner. I hope???