If you live with cats, you may have occasionally seen them doing something funny with their mouths. Sometimes a housecat will stand very still, hold its jaw slightly open, flare its nostrils and seem to be staring at nothing at all. Big cats, like tigers, may even let their tongues hang way out as well. Just what are these cats up to?
Cats have five major sense organs, just like humans - eyes, ears, nose, tongue, and skin - but they also have a sixth sense organ, known as the "vomeral-nasal organ," located on the roofs of their mouths. The vomeral-nasal organ can be thought of as a second nose. It is specifically used by cats to sense a particular kind of odor called a pheromone. Pheromones are chemicals secreted in the sweat of animals that give important information to other members of their species-information such as This Is Who I Am, I Am Friendly, I Am Male or Female, I Am Looking For A Partner-or, conversely, This Is My Space And You Had Better Go Away.
When cats "do flemen", as it is called, they are drawing air slowly into their mouths so that the pheromone-containing odor of other cats will cross the vomeral-nasal organ. Often you will see them doing it around your clothes, especially if you have been holding another cat. If the pheromone they sense is upsetting to them, you may see them become agitated, perhaps raising the fur along their backs while the odor dissipates. If, however, once they have "smelled" the information they feel they are not in any danger, they will close their mouths again and go back to that usual, and inscrutable, expression.