You may occasionally notice your cat making a strange face – a lip-curling grimace with the mouth half open, a wrinkled nose, and a raised chin. The look is usually accompanied by a hypnotic stare, appearing as if the cat is mesmerized. This response is known as Flehmen. You may find it somewhat disconcerting, but fear not, your cat only makes this face when he wants to get a better smell of something in the air, usually the pheromonal odor of another cat.
Pheromones are substances produced by animals that act as a form of chemical communication. In cats, different glands secrete different pheromones that affect a number of behaviors. For example, pheromones help in the attraction of a mate and provide information about a cat's reproductive status. They also are used to mark objects and territory and some promote a sense of well being or familiarity. Pheromones are akin to fingerprints in humans, and their deposition serves as a calling card of sorts.
When your cat exhibits the Flehmen response, it is to open the vomeronasal organ, or Jacobson's organ, a tiny cigar-shaped organ located in the roof of the mouth. This organ is thought to supplement the olfactory system and is especially concerned with the detection of pheromones. Larger cats, such as lions and cougars, a few mammals (including horses), a few bats, and all snakes have the vomeronasal organ and employ the same Flehmen response.
Both male and female cats employ the response in areas where other cats have marked the territory by spraying. It is thought that Flehmen provides information about the identity of the cat that left the scent, whether or not it is a stranger, and what is its sex and reproductive status. By Flehmen, males can determine whether a female is in estrus and therefore ready to mate.
Your cat evolved as a hunter with many keen senses, but of all the senses, his sense of smell is superior; especially up close, and it is one of the ways he navigates around his environment. So when your kitty makes his funny face, keep in mind that he is merely exhibiting another marvelous part of his genetic make-up handed down from his erstwhile feline ancestors. And that's nothing to sniff about.