If you’ve ever seen a horse curl its upper lip and expose its teeth after smelling something, you may have wondered if it was smiling. In reality, this unusual expression is called the Flehmen response, and it’s a completely natural behavior.
When a horse detects an interesting scent—especially one left by another horse—it raises its upper lip to help draw odor molecules toward a special sensory organ called the vomeronasal organ, or Jacobson’s organ. This allows the horse to gather more detailed chemical information than it can through normal smelling alone.
Stallions often display the Flehmen response after smelling a mare, but mares and geldings can do it too. Horses may also curl their lips after investigating unfamiliar objects, other animals, or strong scents around the stable.
Although it looks funny, showing their teeth during the Flehmen response isn’t a sign of aggression or discomfort. Instead, it’s simply one of the fascinating ways horses explore and understand the world around them using their incredible sense of smell.
