In the middle ages did they really throw criminals and disobediant slaves and whatnot into pits of vermin (snakes and rats mostly i’ve heard?)
Band na …
No, I don’t say it.
I think it’s mostly a figure of speech. Many jails were located in cellars and the lower levels of buildings, simply because they were the least desirable and usable areas in the days before electric lights and ducted air. Similarly prisoners on ships were commonly held in the lower damp dark levels. These areas would also be infested with rats and, in warmer areas, cockroaches. This is still true of many third world jails. Being thrown into a rat infested dungeon was simply way if saying that the dungeon was pretty grim.
Never heard of anyone being thrown into a snake pit outside of Indiana Jones.