According to researchers, the peculiar expression on a cat’s face is the result of analyzing chemical signals in their environment. Many animals, including both wild and domestic cats, release pheromones—chemical signals used for communication within their species. To detect and decode these invisible messages, cats rely on a specialized sensory organ in their mouths known as the vomeronasal organ, or the “Jacobson’s organ.” This organ is separate from the olfactory system, which picks up scents but not pheromones, explained cat behavior consultant Alex Taylor to Live Science. He noted that when a cat encounters pheromones, it processes them differently than regular smells. The animal instinctively slightly opens its mouth, displaying a behavior known as the “Flehmen response.” This expression helps pheromones move toward the vomeronasal organ. “It may look like the cat is grimacing, but there’s no emotional aspect to this behavior—the animal is simply detecting and processing pheromones,” Taylor remarked.
Cats use pheromones to convey various messages: for instance, they mark their territory without engaging in fights or strengthen the bond between mothers and their kittens. Pheromones also communicate information about reproductive status, indicating when a female cat is in heat, said Mikel Delgado, a senior researcher at Purdue University’s College of Veterinary Medicine. According to Alex Taylor, pheromones are secreted by specialized glands located in various parts of a cat’s body, such as the chin, cheeks, lip edges, base of the tail, and the area between the eyes, ears, and paws. When cats rub their faces against furniture, scratch surfaces, spray urine, or defecate, they leave chemical messages for other cats. Those cats then use their vomeronasal organ to analyze the detected scent markings and gather information, Delgado explained.
During the Flehmen response, pheromone molecules enter a cat’s mouth—either through licking or inhalation—and dissolve in saliva. They then pass through two channels in the roof of the mouth known as the nasopalatine ducts, leading to a pair of fluid-filled sacs in the vomeronasal organ, Taylor described. When the pheromone molecules reach these sacs, they trigger nerve signals that travel to specific areas of the brain, particularly the amygdala and the region that controls sexual, feeding, and social behaviors. Thus, the chemical signals detected by the vomeronasal organ directly influence a cat’s behavior. According to a study published in the Journal of Comparative Physiology A, while responses to pheromones are automatic, they can still be affected by factors such as the cat’s development, environment, past experiences, and hormone levels.
The vomeronasal organ is not unique to cats. Many animals, from rodents to reptiles, also use it to detect pheromones. “The advantage of Jacobson’s organ is that animals can detect a broader range of molecules in their environment,” explained Jonathan Losos, an evolutionary biologist at Washington University in St. Louis. “Cats have three times as many different scent detectors in their Jacobson’s organ as dogs do,” he added. For cats, the vomeronasal organ is a powerful tool that helps them interpret crucial social information. “Cats are a mysterious bunch. There’s more going on in their heads than we think,” wrote Walter Scott long ago.