Why Do Cats Open Their Mouth After Smelling?

What the Flehmen Response Looks Like

A cat performing the flehmen response often pauses after smelling something, lifts its head, and parts its lips. It may look as though the cat is grimacing, laughing, or reacting to a bad smell. The expression can last several seconds, then the cat returns to ordinary sniffing or moves on.

The mouth is usually only partly open, and the cat may appear focused rather than distressed. Some cats show the behavior more noticeably than others. It is common to see it after a cat sniffs a particular spot, an unfamiliar object, another animal, or something carrying a strong scent.

Flehmen is not the same as panting. During flehmen, the cat generally pauses to assess a smell and briefly holds its mouth open. Panting involves repeated, relatively fast breaths with the mouth open. A cat that is panting, struggling to breathe, or showing other signs of distress needs prompt attention from a veterinarian; do not assume that ongoing open-mouth breathing is just scent investigation.

How Cats Process Interesting Scents

Cats rely heavily on smell, but their scent-processing system does more than detect ordinary odors. They also gather chemical information from substances left by other animals, including scent marks. These chemicals can carry clues about the animal that left them and the context in which the scent was deposited.

When a cat encounters a scent worth examining, it may sniff first and then make the characteristic open-mouth expression. The position of the lips and tongue helps move scent-bearing air or fluid toward the vomeronasal organ, also called Jacobson’s organ. This paired sensory structure sits in the roof of the mouth, behind the front teeth, and connects with parts of the brain involved in interpreting chemical signals.

Ordinary smelling and the vomeronasal system are related but not identical. The nose detects many airborne odors; the vomeronasal organ is specialized for certain chemical cues. The flehmen response helps the cat sample those cues more effectively. It is not simply “smelling with the mouth,” and the open jaw does not mean the cat has stopped using its nose.

Why a Cat Might Do It

The response is especially associated with investigating scents that may contain social or reproductive information. A cat might use it after encountering urine or other scent marks, or after smelling a place another cat has rubbed against. Flehmen can also occur when a cat examines a new or unusual odor, although not every interesting smell triggers it.

Examples include:

A cat sniffing a spot where another cat has urinated or rubbed its face.
A cat investigating a shoe, bag, or object that carries unfamiliar outdoor scents.
A cat smelling a blanket or another item associated with a different animal.
A cat pausing over a scent mark during exploration of its surroundings.

It is not possible to identify exactly what a cat has detected just from its facial expression. The response tells you that the cat is examining chemical information, not whether it has recognized a particular animal or reached a specific conclusion.

Flehmen, Teeth Chattering, and Other Reactions

People sometimes confuse flehmen with teeth chattering, gagging, or a sign of disgust. These behaviors can look similar from a distance, but they are different actions. Flehmen is a still, deliberate-looking pause with the lips parted. Chattering involves repeated jaw movements or quick clicks, and may happen when a cat watches prey or reacts to another stimulus. Gagging involves retching-like movements and is not the usual scent-investigation posture.

A cat may also lick its lips or briefly open its mouth after tasting or smelling something. Context matters: what the cat was doing just before, whether the behavior stops quickly, and whether the cat otherwise seems comfortable all help distinguish a normal sniffing response from a possible problem.

One common misconception is that cats make this face because a smell is necessarily unpleasant. A cat may perform flehmen in response to a scent that is compelling or informative, not merely foul. The expression can look comical to people, but it is a way of gathering sensory information.

When Open-Mouth Behavior Needs Attention

A brief flehmen response after sniffing is generally normal behavior. The more important distinction is whether the cat is investigating a scent or breathing with its mouth open. Cats do not ordinarily pant as routinely as dogs, so persistent or repeated open-mouth breathing should not be dismissed as a funny face.

Contact a veterinarian if open-mouth breathing continues or occurs with signs such as labored breathing, weakness, collapse, unusual drooling, or an apparent inability to close the mouth. These signs can have different causes, and only a veterinarian can assess them. If you are unsure whether you are seeing flehmen or breathing difficulty, treat the concern seriously and call a veterinary clinic for guidance.

Likewise, if the mouth-opening behavior appears painful, happens repeatedly without a clear scent-related trigger, or comes with a sudden change in eating or behavior, contact a veterinarian. Do not try to diagnose the cause from the facial expression alone.

Frequently Asked Questions

Why does my cat open its mouth after smelling my shoes?

Shoes can carry a mixture of unfamiliar scents from people, animals, and places. Your cat may be using the flehmen response to examine chemical cues in that scent; the expression does not reveal exactly what it has detected.

Does a cat open its mouth because something smells bad?

Not necessarily. Flehmen is a scent-investigation behavior, not a reliable sign of disgust. Cats may use it to examine interesting or socially meaningful odors.

Do all cats perform the flehmen response?

Many cats show it, but it may be subtle or uncommon in an individual cat. Not seeing the behavior does not by itself indicate a problem.

Is flehmen the same as panting?

No. Flehmen is usually a brief pause after smelling, with the lips parted while the cat investigates a scent. Panting is repeated open-mouth breathing; if it persists or looks labored, call a veterinarian.

How long should the open-mouth expression last?

Flehmen is typically brief and stops once the cat finishes investigating. Ongoing open-mouth breathing or a repeated expression unrelated to sniffing deserves a call to a veterinarian, especially if the cat seems unwell.

Further reading: Cornell Feline Health Center. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.