Why Do Cats Open Their Mouths When They Smell Something?

Why Do Cats Open Their Mouths When They Smell Something?

A cat’s keen sense of smell can be troublesome, leading her to follow a urine trail into another cat’s “territory” or experiment with mystery food scraps in the garbage can. Yet, nothing beats that unmistakable grimace on your kitty’s face, with mouth hanging wide-open, as she takes a whiff. You can’t help but question: why do cats open their mouths when they smell something?

Cats open their mouths when they smell something because of the flehmen response. This sneer allows the aroma to enter the mouth, where the cat transfers the scent to the vomeronasal organ. Cats used this smell/taste mechanism to further investigate appetizing aromas or pheromones from other cats.

Rest assured, that concerning grimace on your kitty’s face isn’t a sign that your cooking is offensive or that your cat’s feeling particularly angsty. To learn about why cats open their mouths as they explore a new environment with their noses (AKA: stinky face), read on!

What Is the “Flehmen” Response?

That unusual stink face your cat makes while smelling something has a name: the flehmen response. The word “flehmen” translates to “look spiteful” or “to bare the upper teeth” in different German tongues. Let’s take a look at what this bizarre snarl looks like and how it works.

Why Do Cats Open Their Mouths When They Smell Something?

What Does the Flehmen Reaction Look Like?

With the unfortunate reputation for being malicious and flat-out unpredictable, cat owners assume this unusual feline face is more devious than anything, using descriptors like:

  • Sneering
  • Grimacing
  • Lip curling
  • Mouth gaping
  • Smirking

The flehmen reaction is anything but sinister, and your cat is undoubtedly not plotting against you. When that flehmen reaction kicks in, a cat will curl its top lip upward, wrinkle its nose, bare its front teeth, inhale deeply, and flick its tongue.

This goofy expression typically lasts a few seconds (or the length of a hearty whiff), but some kitties hang their mouths open a bit longer — almost as if they’re panting or out of breath.

How Does the Flehmen Response Work?

It’s no coincidence that your cat’s mouth gapes open as she inhales near the litter box or on a grassy patch in the yard. This flehmen response connects (and further amplifies) a cat’s robust sense of smell. Here’s a glimpse at how this process looks:


A curious kitty will follow her nose until she finds something that catches her attention, whether that’s a seemingly bare spot on the wall or an empty ceramic bowl from supper. A cat will lean in and “breathe” the aroma in via her nostrils and mouth. In this initial stage, you’ll notice the distinguished lip curl and exposed teeth — a true flehmen!

Tongue Flicking

If you look closely, you’ll see that your cat is flicking her tongue up and down as she sniffs — a bizarre sight to behold. This flicking motion transfers the scent from the tongue to the vomeronasal organ (Jacobson’s organ) located in the roof of the mouth.

The small ducts nestled behind the top row of teeth connect to the brain, allowing the cat to decipher what this strange smell could possibly suggest.


Drawing the aroma into the mouth and the vomeronasal organ nearly doubles the sensory experience. While a cat’s taste receptors significantly lag, their sense of smell could be 14 times more powerful than humans’.

Thanks to the flehmen response, a cat can accurately “taste” another cat’s pheromones or another mysterious aroma while redirecting this sensory response to the reliable olfactory receptors instead.

Are you still a little curious about your kitty’s mysterious “stink face” and why cats make it? The Jackson Galaxy video below will delve a little deeper into this bizarre feline behavior:

What Makes a Cat’s Flehmen Reaction Kick In

The flehmen reaction (and its accompanying mouth gape) heightens a cat’s sense of smell and ability to “read” a chemical message. However, cats don’t always open their mouths when they sniff something. Let’s talk about instances where a cat’s flehmen response comes in handy.

Pheromone Detection and Mating Desires

Your kitty’s smell may not be distinct or recognizable to you, but all cats leave behind unique scents — sometimes called “pheromones” — as they go about their travels. Cats deposit these coded chemical messages when they knead a blanket, rub their faces against an owner’s leg, or spray a “territory.” Scent marking is a cat’s way of saying, “This is mine … back off!”

A persistent flehmen reaction is a cat’s way of learning about a mysterious kitty who recently ventured this same path, but it’s what a tomcat can learn about a queen with this mechanism that shocks humans. These pheromones can reveal whether a female cat is in heat and fertile.

When an unneutered male cat detects this mating opportunity, he’ll desperately yowl and cry to get this female cat’s attention. As such, it’s far more common for male cats to open their mouths when sniffing than females, at least when it’s for pheromone detection.

Identifying Kittens

Female cats may not exhibit a flehmen response to the same tune as males, but they’re no strangers to this unusual and eye-catching snarl. A queen with a new litter will use this reflex to identify each of her kittens’ distinct scents. This high-definition scent detection allows a mother cat to better track her kittens and ensures they’re not straying too far from her care.

Exploring the Environment

Most often, a cat’s flehmen response stems from a pheromone investigation and a desire to socialize. However, cats can rely on this sensory tactic to learn more about any intriguing smell and remain “in-tune” with their environment, such as:

  • Food scraps, grease, or crumbs
  • Catnip
  • A water or food bowl
  • A new bed, blanket, or piece of furniture
  • Shoes, toothbrushes, or hairbrushes (where you leave your scent)

Some cats have a habit of these in-depth inhales, even in the absence of pheromones or a newborn litter. It’s nothing more than curiosity, personality, and a habit.

The Flehmen Response on Other Species

Unless you’re a zookeeper or a loyal animal sanctuary visitor, your cat’s first flehmen reaction will probably be quite surprising. However, domestic cats aren’t the only species to offer a lip curl when a particular scent piques their interest. Other known species with this ability include:

  • Horses
  • Buffalos
  • Giraffes
  • Hedgehogs
  • Pandas
  • Tigers
  • Rhinoceroses
  • Hippopotamuses
  • Llamas

In the animal kingdom, this flehmen response wouldn’t exist if it weren’t for scent communications. All of the above species send chemical messages (pheromone deposits) when they urinate in the open. These “marking” behaviors allow animals to signal that they’re ready to mate or claim a certain territory. The resulting flehmen is a way to “read” the signal.

Despite this shared reflex and ability to communicate via scent, scientists have yet to discover if the flehmen response is cross-species. That is, whether a cat can dissect and understand a panda’s pheromones (or a tiger and rhinoceros), for example. While there is no evolutionary purpose for this skill, it sure would be interesting.


As odd as that face-mangling lip curl looks, it’s an entirely normal response for a curious kitty looking to explore. However, understanding why your cat’s flehmen response kicks in can help you better understand what intrigues her. You may just discover that one of your beloved felines is spraying your interior walls or which meat your carnivorous kitty seems to crave most.

Don’t forget to snap a photo of those flehmens to remember for years to come. It’s not every day you get to see your kitty do something quite so humorous.