Flehmen response

The flehmen response (/ˈfleɪmən/; German: [ˈfleːmən]), also called the flehmen position, flehmen reaction, 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. It may be performed over a site or substance of particular interest to the animal (e.g. urine or faeces) 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. The behaviour 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.

The word originates from the German verb flehmen, to bare the upper teeth. It comes from the Upper Saxon German flemmen, "to look spiteful".

An animal may perform the flehmen response when investigating sites of particular interest, or perhaps (more generally) odors or tastes. This response is characterised by the animal curling back its top lip exposing the front teeth and gum, then inhaling and holding the posture for several seconds. The behavior may be performed over particular locations, in which case the animal may also lick the site of interest, or it may be performed with the neck stretched and head held high in the air for a more general gustatory investigation. The flehmen response often gives the appearance that the animal is "grimacing", "smirking" or "laughing".

The main function of flehmen is intraspecific communication by transferring air containing pheremones and other scents to the VNO, an olfactory chemosensory organ located between the roof of the mouth and the palate. This provides chemical cues which animals use in a variety of ways.

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