What behavior characterized by curling back the upper lip is known as?

The behavior characterized by curling back the upper lip is known as the Flehmen response. This is a unique behavior observed in many animals, including horses, where they curl back their lips to expose the vomeronasal organ, which helps them detect pheromones and other chemical signals in their environment. This response allows the animal to assess scents more effectively, particularly those related to reproduction, social interactions, and territory.

This behavior is an instinctual reaction that aids in communication and understanding within a species. It is not related to predatory, pack, or defensive behaviors, which involve different instincts and responses to the environment or threats. The Flehmen response is specifically associated with sensitivity to chemical signals, making it significant in understanding animal behavior and social structures among equines and some other mammals.