The Flehmen Response: Why Cats “Grimace” with Their Mouths Open

cat with mouth open
Cat, Peter Heeling, Wikimedia Commons

Many animals (including horses, buffalo, llamas, and tigers) have a sensory organ called the Jacobson organ (or vomeronasal organ) that enables them to gather more information about scents through the roofs of their mouths. A cat that is using this organ will open his mouth and make an odd face, as though he is sneering, grimacing, or frozen with his mouth slightly open, as he draws air into the organ to check it. Many people mistakenly assume that the cat is disgusted when he does this, because he may wrinkle up his nose in a way that a human would if encountering an unpleasant smell. This “grimace” is known as the Flehmen response.

The Jacobson organ, which is connected to areas of the brain associated with sexual, social, and feeding behaviours, is most often used by male cats to determine the sexual status of local females – in other words, to discover whether they are fertile and ovulating by the scent of their urine. However, both female and male cats display the Flehmen response when encountering a variety of scents.

It has been speculated that in addition to determining whether females are in heat, cats may be able to gather information regarding the physiological states of many different of animals using the Flehmen response, which can assist with predatory activities. Also, because cats may engage in the Flehmen grimace in response to interesting plant scents such as catnip, this extra sense may have broader applications, but more research is required to fully understand all of its uses.

For more cat articles, see the main Cats page.


    • Tabor, R. (2005). 100 Ways to Understand Your Cat. Cincinnati, Ohio: David & Charles.
    • Case, L.P. (2003). The Cat: It’s Behaviour, Nutrition, and Health. Ames, Iowa: Iowa State Press.

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