Rat kings are phenomena said to arise when a number of rats become intertwined at their tails, which become stuck together with blood, dirt, ice or excrement or simply become knotted. The animals reputedly grow together while joined at the tails. The numbers of rats that are joined together can vary, but rat kings formed naturally from a large number of rats are rarer. The phenomenon is particularly associated with Germany, where the majority of instances have been reported. Historically, there are various superstitions surrounding rat kings, and they were often seen as a bad omen, particularly associated with plagues.