Instinct & Normal Cat Behavior: Flehmening
Sensing Smell With an Open Mouth

Why Does Your Cat Sometimes Open its Mouth to Smell?

Flehmening occurs when your cat smells something and then opens its mouth slightly, wrinkles his nose, and curls back his upper lip. The ears also become flattened in some cats. This apparent grimace is also called the 'flehmen reaction' (sometimes also known as 'flehming'). The cat draws in air, capturing the scent, and transferring it to a small specialized sac called the 'vomeronasal organ' or 'Jacobson's organ.' This organ is located high up in the roof of the mouth, and has a large blood supply. It traps the odor molecules and sends signals to the brain regarding the scent.

It is easy to see flehmening as a reaction against a bad odor when it is actually just the opposite. When a cat sniffs a sharp smelling chemical, such as those in some household cleaners, heavily spiced foods or citrus scents, it turns away or draws back quickly to get away from the odor. The Flehmen response is just the opposite. The cat wants additional information from the odor.

Flehmening can occur with a number of scents, but most frequently occurs when the cat smells urine. Many male cats will exhibit this behavior when they smell the genitals or urine of a female cat in heat.

If you want to have some fun with your cat's sense of smell, take some small bits of different things, such as a bit of chicken, a cotton ball with some flowery perfume, a fragrant flower and, to make things interesting, a piece of smelly cheese -- such as aged blue cheese. Place each different scent under a piece of paper towel (so your cat cannot see the item) and encourage your cat to investigate. Watch him sniff. Did you see him flehmening? What piqued his interest the most?

Mammalian Vomeronasal Organ

The diagram shows the position and connections of the Vomeronasal Organ in a rodent (hamster) to illustrate the general organization in mammals. The diagram shows the left Vomeronasal Organ located within a longitudinal bulge along the base of the left side of the nasal septum. There is a paired organ on the right side (not shown). Vomeronasal sensory neurons are located in a sensory group of cells, resembling the main cell-group that provide the sense of smell but separated from it, lining an elongated cavity (lumen) inside the thin bone capsule that encloses the organ. A narrow duct, opening onto the floor of the nasal cavity just inside the nostril is the only access for stimulus chemicals. Mammalian vomeronasal sensory neurons detect specific chemicals, some of which may act as chemical-communication signals (pheromones) from other individuals of the same species, and trigger the generation of electrical impulses that carry the information to the brain. The Vomeronasal Organ is not the exclusive chemosensory organ capable of detecting pheromones. There are some examples where the main olfactory system (sense of smell) mediates pheromone communication.

There are three hypotheses on the exact function of the Vomeronasal Organ. The first is to perceive the smell of food; the second, as a "sixth sense" to help predict unusual occurrences, e.g., earthquake, volcanic eruption; and the third is for perception of sexual odors - pheromones.