Tail-rattling in rodents: more than a threat display.

One of the most peculiar behaviors of rodents is tail-rattling, a rapid vibration of the tail which can produce a rattling sound when performed against a hard surface. Tail-rattling is widespread across rodents, having been observed in 32 species from 19 genera, including Mus and Rattus. Rodent tail-rattling has been known from the eighteenth century, when it was described as part of the defensive behavior of the crested porcupine. From the 1940s, comparative psychologist John Scott systematically studied tail-rattling in laboratory mice, making it widely popular among laboratory researchers as one of the main components of the mouse agonistic ethogram. Currently, tail-rattling is interpreted almost exclusively as a threat display. However, historically, tail-rattling has been described in a great variety of different contexts, including intraspecies agonism, antipredator behavior, male-to-female courtship, female proceptive behavior, caressing by a human caregiver, social isolation, home-cage change, footshock-induced fear and decisional conflict. This wide range of contexts indicates that tail-rattling is not just a sign of aggressiveness, but can be associated with a set of emotions comprising anger, fear, distress, uncertainty, sexual arousal and physical pleasure. Notably, tail-rattling is expressed by rodents in emotional contexts of both negative and positive affective value. In the present article, firstly we provide a historical overview of rodent tail-rattling observations, starting from porcupines and ending with mice, covering a period from the 1770s to 2026. We then discuss what emotional state tail-rattling may express. Subsequently, we evaluate the possible functions of rodent tail-rattling. Additionally, we present our explanatory model of tail-rattling, the discharge model. Finally, we propose future directions for rodent tail-rattling research, including the employment of tail-rattling as a marker of animal welfare in laboratory and zoo rodents.