Flehmen response

The flehmen response (/ˈfleɪmən/; from German flehmen, to bare the upper teeth, and Upper Saxon German flemmen, to look spiteful), also called the flehmen position, flehmen reaction, flehmen grimace, flehming, or flehmening, is a behavior in which an animal curls back its upper lip exposing its front teeth, inhales with the nostrils usually closed, and then often holds this position for several seconds.^[1] It may be performed over a sight or substance of particular interest to the animal, or may be performed with the neck stretched and the head held high in the air.

Flehmen is performed by a wide range of mammals, including ungulates and felids.^[1] The behavior facilitates the transfer of pheromones and other scents into the vomeronasal organ (VNO, or Jacobson's organ) located above the roof of the mouth via a duct which exits just behind the front teeth of the animal.