The flehmen response (ˈfleɪmən, ˈfleːmən), also called the flehmen position, flehmen reaction, flehming, or flehmening (from German flehmen, meaning to curl the upper lip), is a particular type of curling of the upper lip in ungulate

Ungulate

Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...

s, felids, and many other mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, which facilitates the transfer of pheromone

Pheromone

A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...

s and other scents into the vomeronasal organ

Vomeronasal organ

The vomeronasal organ , or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It was discovered by Frederik Ruysch and later by Ludwig Jacobson in 1813....

, also called the Jacobson's organ.

Exhibition

In the flehmen response, animals draw back their lips in a manner that makes them appear to be "grimacing" or "smirking". The action, which is adopted when examining scents left by other animals either of the same species or of prey, helps expose the vomeronasal organ and draws scent molecules back toward it. This behavior allows animals to detect scents, for example from urine, of other members of their species or clues to the presence of prey. 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 recognizable, for example, in stallion

Stallion (horse)

A stallion is a male horse that has not been gelded .Stallions will follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone may give stallions a thicker, "cresty" neck, as well as a somewhat more muscular physique as compared to...

s when smelling the urine of a mare in heat. To detect estrus the male giraffe's flehman response includes the actual taste-testing of the female's urine.

Cats, especially house-cats, exhibit a natural and very noticeable teeth-baring grin — the Flehmen response — in order to draw scent into the Vomeronasal organ

Vomeronasal organ

The vomeronasal organ , or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It was discovered by Frederik Ruysch and later by Ludwig Jacobson in 1813....

. The organ and its purpose was discovered in 1813, although cat owners have always observed the behavior.

This behavior is not limited to predators. Horses have been well known to exhibit flehmen response.

Physiology

The vomeronasal organ

Vomeronasal organ

The vomeronasal organ , or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It was discovered by Frederik Ruysch and later by Ludwig Jacobson in 1813....

, also called Jacobson's organ, is a chemoreceptor organ believed to play a role in the perception of certain scents and pheromones. It is named for its closeness to the vomer

Vomer

The vomer is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.-Biology:...

 and nasal bone

Nasal bone

The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....

s, and is particularly developed in animals such as cat

Cat

The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...

s and horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s. The organ is located on the roof of the mouth. In addition to
house cats
and horses, animals who exhibit the flehmen reaction include
buffalo

American Bison

The American bison , also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds...

,
tiger

Tiger

The tiger is the largest cat species, reaching a total body length of up to and weighing up to . Their most recognizable feature is a pattern of dark vertical stripes on reddish-orange fur with lighter underparts...

s,
tapir

Tapir

A Tapir is a large browsing mammal, similar in shape to a pig, with a short, prehensile snout. Tapirs inhabit jungle and forest regions of South America, Central America, and Southeast Asia. There are four species of Tapirs: the Brazilian Tapir, the Malayan Tapir, Baird's Tapir and the Mountain...

s, lion

Lion

The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...

s,
giraffe

Giraffe

The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...

s,
goat

Goat

The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...

s,
llama

Llama

The llama is a South American camelid, widely used as a meat and pack animal by Andean cultures since pre-Hispanic times....

s and
kob

Kob

The Kob is an antelope found across Sub-Saharan Africa from Senegal to South Sudan. Found along the Northern Savanna, often seen in Murchison Falls and Queen Elizabeth National Park, Uganda; Garamba and Virunga National Park, Democratic Republic of the Congo, as well as grassy floodplains of...

s.

Similar responses

A grimace similar to the flehmen response may also be seen in association with pain. In horses, it is often associated with low-grade abdominal pain.

Further reading

• Swaisgood, R. R., D. G. Lindburg, X. Zhou, and M. A. Owen. 2000. The effects of sex, reproductive condition and context on discrimination of conspecific odours by giant pandas. Anim. Behav. 60; 227-237.