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The Flehmen Response in Domestic Cats

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A. Golden is a writer and editor living in Alabama. They graduated with a B.A. in English.

A cat making the flehmen response.

A cat making the flehmen response.

What Is the Flehmen Response?

Have you ever seen your cat make an odd expression akin to a grimace or sneer? It’s hard to miss when it happens. The nose wrinkles, the upper lip draws back, and their mouth opens and remains slightly ajar for a short time.

Contrary to its appearance, this comical face is not your kitty expressing disgust; it is a biological behavior known as the flehmen response.

Derived from the German verb “flehmen,” roughly meaning “to curl the lip,” the response functions as a way for cats to gather additional sensory information.

This behavior isn’t limited to domestic cats. Felids of all kinds exhibit the response, as well as many other animals: horses, giraffes, goats, buffalo, sheep, and deer, to name just a few.

When a cat exhibits the flehmen response, they are not recoiling from an odor but rather investigating it further. So how does this physiological mechanism work, and what purposes does it serve?

A Siberian tiger demonstrating the flehmen response.

A Siberian tiger demonstrating the flehmen response.

Anatomy of the Flehmen Response

The flehmen response is made possible by a specialized sensory structure called the vomeronasal organ, or the Jacobson’s organ.

The vomeronasal organ consists of two fluid-filled sacs located in the roof of the mouth. The nasopalatine canal—two small ducts situated just behind the front teeth—connect these sacs to the nasal cavity, forming a passageway for scents.

The rather silly-looking gape cats adopt during the response is what allows them to draw odors into the mouth rather than the nose. The vomeronasal organ then analyzes the scent, transmitting information to the cat’s brain.

In the context of senses, the flehmen response is difficult for us as humans to describe, as we lack the structures necessary to experience it. However, it is believed that the process is something akin to a hybrid between smell and taste.

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But enough about the mechanics of the response—why do cats actually do it?

What Is Its Function?

In cats, the flehmen response is most commonly used in the detection and inspection of pheromones—chemicals animals use to communicate among their own species. Cats typically distribute pheromones in the form of urine marking or face rubbing.

On average, male cats utilize the response more frequently than females do, usually for mating purposes. Pheromones are particularly valuable for breeding, providing details on a cat’s sex, age, location, and reproductive status. By engaging in the response, a tomcat can ascertain whether or not a female is in estrus (heat) and thus in an ideal condition for mating. Female cats sometimes use the flehmen response when familiarizing themselves with the scent of their newborn kittens.

The response isn’t solely used in relation to pheromones, though. Any odor a cat finds interesting, unfamiliar, or novel can prompt the behavior. This varies with each individual cat and ranges from plants (especially catnip) to food to household objects.

In the video below, an electric toothbrush elicits the response from a curious Abyssinian cat.

The intense reaction catnip incites in many felines comes from the plant’s active ingredient, nepetalactone. One study suggests that nepetalactone simulates pheromones, which would explain why so many cats show the response around it.

This is where the details get murky. The link between the flehmen response and pheromones is relatively straightforward, but we're not sure why exactly cats perform the response around so many miscellaneous objects—such as the electric toothbrush seen above. Research on the behavior is still ongoing.

For now, though, we can at least appreciate this fascinating biological phenomenon and enjoy the ridiculous facial expressions it produces.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2018 A Golden


K S Lane from Melbourne, Australia on April 13, 2018:

Really interesting read! I've always wondered why my cats do this!

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