What does the term "flehmen response" refer to in horses?

The term "flehmen response" specifically refers to the behavior of curling the lip, which allows horses to better assess scents and pheromones. When a horse curls its upper lip and opens its mouth, it enables the vomeronasal organ, located in the roof of the mouth, to detect and analyze different chemical signals in their environment. This behavior is often observed in stallions when they are investigating the scent of a mare in estrus or other novel odors, indicating its role in social and reproductive behavior.

This unique physiological response plays an essential part in communication and environmental awareness for horses, highlighting their reliance on olfactory cues. The flehmen response reflects a horse's instinctual behavior and demonstrates their sensitivity to chemical signals, which is crucial for survival and social interactions in the wild.