Rat corpses are treated as “treats” (highly desired food) for the purpose of feeding them to cats.

Based on Dracula’s association with rats, Vlad’s Tower should have a horde of r monsters somewhere in it, and/or increase the spawn rate for r monsters.

Storeroom: a special room that only generates in a dead end room, perhaps only if the room is under a certain total area. Contains 2-4 chests or large boxes, and rarely ice boxes. If the game had barrels, it should have some of those too. May contain a couple rats too.

Improvising on a wooden flute may compel all r monsters (or just the rats) within its audible range (or the whole level) to move closer to you or follow you, a reference to the Pied Piper of Hamelin.

Some monsters’ corpses, like rats, have a chance of conferring FoodPois when eaten, regardless of whether they are tainted.

Rat king (a randomly generated monster, not the SLASH’EM unique Rat King), based on the real-life rat king. It is a r, not much faster than a rock mole, but has several bite attacks (possibly scaling the amount by monster level). Each bite has a small chance of conferring disease. Its level corresponds to the number of entangled rats, so a slashing attack could sometimes cut off one rat, which then appears on the floor as a new rat, and makes the rat king lose a level.

Baluchitheria and other elephant-like q flee from small rodents like sewer rats.