The Flehmen Response in Cats: Decoding Feline Scent Behavior
If you've ever seen your cat pause, curl its upper lip, bare its front teeth, and hold its mouth slightly open after sniffing something intriguing, you've witnessed the flehmen response. Sometimes called the "stinky face" or flehmen grimace, this quirky feline behavior is more than just a funny expression—it's an essential part of how cats interact with their world.
What Exactly Is the Flehmen Response?
The flehmen response is a deliberate action where an animal (not just cats!) curls back its upper lip, exposes its front teeth, and inhales—often with nostrils closed. The pose typically lasts only a few seconds but serves an important purpose: processing specific scents that carry vital information. You'll see this behavior not just in house cats but also in horses, goats, tigers, lions, sheep, tapirs, zebras, giraffes, rhinoceroses, elephants, antelope, hedgehogs—the list goes on.
How Does It Work?
When a cat enacts the flehmen response:
- It holds its mouth open and curls its upper lip.
- This exposes the front teeth and sometimes causes squinting or wide eyes.
- The position allows air and scent molecules to pass through a special sensory organ called the vomeronasal organ (VNO), or Jacobson’s organ.
The VNO sits at the base of the nasal cavity. Most animals that show flehmen have an opening on the roof of their mouth behind their front teeth; this connects to ducts that send scent molecules directly to the VNO. Here, pheromones and hormones—chemical messengers from other animals—are processed as a sensation that's part smell and part taste.
Why Do Cats Do It?
Cats use the flehmen response to analyze chemical signals found in:
- Urine or scent markings
- Pheromones from other cats (especially males detecting females in heat)
- Kittens’ scents for mother cats tracking their young
- New or strong-smelling objects like catnip or unfamiliar foods
- Household items carrying outdoor smells (shoes or bags)
You’ll most often spot this behavior where scents are concentrated: litter boxes, doorways marked by other cats, or objects that have been recently sniffed by another animal. The flehmen response helps cats decode messages about territory boundaries, reproductive status, identity of other animals nearby—even emotional states.
The Science Behind Flehmen
The main role of flehmen is intra-species communication. For example:
- A male cat may use it to assess whether a female is ready to mate by sniffing her urine.
- Mothers may track kittens using scent cues processed through flehmen.
The VNO detects non-volatile organic compounds—meaning it needs direct contact with the odor source. Unlike dogs (who also have a VNO), cats appear to have more types of receptors here and show a stronger flehmen reaction.
Flehmen vs. Other Cat Behaviors
It's easy to mistake flehmen for open-mouthed breathing due to distress (like panting), sneezing fits, yawning, or even teeth chattering. But there are key differences:
- The flehmen response is brief—just a few seconds after sniffing something specific.
- Cats don't appear distressed; they're focused and intent.
If you see your cat holding this pose after investigating something new or strong-smelling (not during play or rest), it's almost certainly performing flehmen—not struggling to breathe.
A Widespread Mammalian Trait
This fascinating trait isn't unique to domestic felines. Wild relatives like lions and tigers do it too. Horses exhibit a similar response but process scents differently; their VNOs connect only to nasal passages since they don't breathe through their mouths. Even goats sometimes react to urine from other species—a sign that certain chemicals can trigger cross-species responses among mammals.
Why Is Flehmen Important?
- It enables cats to gather complex chemical messages crucial for social structure and mating behaviors.
- Cats can detect reproductive status among peers without direct interaction.
This behavior supports everything from territory management to synchronizing breeding cycles within groups of animals. It's one reason why scent-marked areas are so important in multi-cat households—and why your cat might make that silly face near another pet's favorite spot!
