The sight of a cat pausing, lifting its upper lip, and holding its mouth slightly open is often mistaken for a grimace caused by a foul odor. This action is purposeful, allowing the cat to engage a specialized sensory system beyond its primary sense of smell. Cats possess an auxiliary olfactory apparatus that uses the mouth not for breathing or tasting, but to analyze complex chemical signals. This secondary system provides the animal with detailed social information that its nose cannot detect alone.
The Distinctive Flehmen Response
When a cat encounters a scent of particular interest, it performs a voluntary action known as the Flehmen response. This behavior involves pulling back the lips, wrinkling the nose, and slightly opening the mouth in a posture that resembles a sneer. The purpose of this action is to channel air and the accompanying scent molecules towards a pair of small ducts located just behind the upper incisor teeth on the roof of the mouth.
This muscular movement effectively seals off the normal nasal passage, ensuring that the scent is directed specifically to the sensory structure. The cat may hold this expression for several seconds, allowing the non-volatile chemical compounds to be drawn in for analysis. This process aids in sophisticated chemical communication and environmental assessment.
Function of the Vomeronasal Organ
The specialized sensory structure is the Vomeronasal Organ (VNO), also known as Jacobson’s organ. This organ is situated within the soft tissue separating the nasal cavity and the mouth, near the vomer bone, and is connected to the oral cavity by the nasopalatine ducts. The VNO is lined with unique sensory receptor cells that are chemically distinct from those used for standard olfaction in the main nasal passages.
Unlike the main olfactory bulb, which processes general smells, the VNO sends its neural signals along a separate pathway to the accessory olfactory bulb in the brain. This pathway bypasses the brain areas associated with conscious smell perception. Instead, the VNO’s signals travel directly to regions like the amygdala and hypothalamus, which govern instinctual and social behaviors, including mating and aggression. The organ is therefore structured to trigger an automatic, internal response rather than a conscious recognition of an odor. This mechanism allows for the rapid, instinctual interpretation of social information.
Chemical Signals Detected
The Vomeronasal Organ detects certain types of molecules that are too heavy or non-volatile to be efficiently inhaled through the main nasal passages. The primary compounds analyzed by this system are pheromones, which are chemical signals released by other animals of the same species. These chemical messages are often deposited in urine, feces, or glandular secretions left on surfaces. Pheromones carry information, such as the reproductive status of another cat, its emotional state, and its individual identity.
For example, a male cat may use the Flehmen response to analyze pheromones in a female’s urine to determine if she is in heat. By contrast, volatile odors, like the smell of food or perfume, are easily airborne and are detected by the cat’s highly sensitive primary olfactory system.