Flehmen response

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The flehmen response, also called the flehmen position, flehmen reaction, flehming, or flehmening, is a particular type of curling of the lips in ungulates, felids, and many other mammals, which facilitates the transfer of odorant chemicals into the vomeronasal organ. In the flehmen reaction, animals draw back their lips in a manner that makes them appear to be "grimacing". The pose, which is adopted when examining scents left by other animals of the same species, helps expose the vomeronasal organ and draws scent molecules back toward it. This behavior allows animals to detect odorants, for example from urine, of other members of their species. Flehming allows the animals to determine several factors, including the presence or absence of estrus, the physiological state of the animal, and how long ago the animal passed by. This particular response is most recognizable in stallions when smelling the urine of a mare in heat.

The vomeronasal organ, also called Jacobson's organ, is a chemoreceptor organ thought to have to do with the perception of certain pheromones. It is named for its closeness to the vomer and nasal bones, and is particularly developed in animals like cats and horses. The organ is located on the roof of the mouth. In addition to housecats and horses, animals that exhibit the flehmen reaction include buffalo, tigers, tapirs, lions, giraffes, and llamas.[1][2][3]

The flehmen response may also be seen in association with pain.[4] In horses it is often associated with low grade abdominal pain.

One human equivalent is the instinctive pulling back of the upper lip when faced with something "disgusting".

[edit] Source

• Pion PD and Spadafori G. The feline behavior series. VeterinaryPartner.com