Reinigen

Reinigens (singular: Reinigen; pronunciation: RY-ni-gin; Germ. reinigen "to clean") are rat-like creatures that exist at the bottom of the Grimm creature food chain. They are similar to rats in that they are scavengers, not being the least bit picky about what they eat, and are rarely violent unless pushed to the limit. They possess a musical ability that enables them to mesmerize and control rats' behavior.

Monroe described them as being "at the bottom of the food chain" and hints at them living on the leftovers of society.