The Flehmen Response in Cats

Posted by
Jennifer Copley
May 2, 2009

Why do cats sometimes stand still with their mouths slightly open and appear to be grimacing or sneering?

Many animals (including horses, buffalo, llamas, and tigers) have a sensory organ called the Jacobson organ (or vomeronasal organ) that enables animals 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 Flehman 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 gauge the sexual status of local females - in order words, to discover whether they are fertile and ovulating by the scent of their urine. However, both female and male cats display the Flehman response when encountering a variety of scents.

It has been speculated that in addition to gauging whether females are in heat, cats may be able to gather information regarding the physiological states of many different of animals using the Flehman response, which can assist with predatory activities. Also, because cats may engage in the Flehman 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.

Sources: 100 Ways to Understand Your Cat by Roger Tabor and The Cat by Linda P. Case, Kerry Helms, and Bruce MacAllister.

For information on why cats do other things such as hissing, purring, urinating outside the box, playing with prey, bringing prey home, fighting, rubbing against things, eating houseplants, and more, see Why Does My Cat Do That?

For more cat facts and statistics, see: