Why Do Cats Open Their Mouths After Sniffing?

What the flehmen response looks like

The familiar expression can look like a grimace, a silent meow, or a cat caught mid-sniff. A cat typically pauses after investigating a smell, raises or slightly curls its upper lip, parts its mouth, and stays still for a few seconds. It may then close its mouth and move on. The posture is generally called the flehmen response, from a German word meaning to curl the upper lip.

Cats do not necessarily make this face every time they smell something interesting. The response is most noticeable when they encounter particular chemical cues, including scents left by other cats. A cat may show it after sniffing a spot where another animal has rubbed or urinated, or after investigating an unfamiliar object. The behavior is a way of gathering and assessing information, not a sign that the cat finds the odor disgusting.

How scent reaches a second sensory system

Ordinary smelling primarily involves odor molecules reaching sensory cells in the nasal cavity. Cats also have a vomeronasal organ, sometimes called the Jacobson’s organ. In cats, this small structure is located in the roof of the mouth and connects with the nasal and oral regions. It detects chemical signals that are not processed in exactly the same way as ordinary airborne odors.

When a cat opens its mouth after sniffing, it can help move scent-bearing air or fluid toward the vomeronasal organ. The cat pauses while that sensory information is being assessed. The face may look dramatic, but the animal is not “tasting” the odor in the ordinary sense, and the open mouth is not simply an attempt to breathe through the mouth.

This system is especially useful for investigating pheromones and other social chemical cues. Such cues can carry information about another animal, though a person watching a cat cannot reliably identify exactly what the cat has detected from its expression alone.

Why cats investigate certain smells

Scent is central to how cats explore their surroundings. Smelling helps them inspect objects, recognize familiar places and animals, and notice changes in their environment. The vomeronasal organ adds another route for examining particular chemical messages, especially those associated with other cats.

For example, a cat might sniff a patch of ground or a piece of furniture where another cat has left scent. It may then lift its head and hold its mouth open briefly. Urine can carry chemical information, but so can scent deposited when cats rub their faces or bodies against objects. The response does not mean the cat is necessarily reacting to urine, nor does it reveal whether the message is about sex, territory, identity, or something else. The specific cue and its meaning cannot be determined just by looking at the flehmen expression.

Domestic cats share this response with other mammals. Horses are especially well known for it, but the behavior occurs in a range of species. Its presence in cats reflects the importance of chemical communication, even in animals that also rely strongly on sight, hearing, and touch.

What it is—and what it is not

A brief, scent-linked open-mouth pause is different from ongoing open-mouth breathing. Cats normally breathe through their noses at rest. If a cat is panting or breathing with its mouth open without an obvious connection to sniffing, that is not something to label as flehmen just because the mouth is open.

The response is also not the same as a cat making a “stink face” because an odor is unpleasant. People often interpret the raised lip as disgust, but the cat is using a specialized scent pathway. It may be intensely curious rather than repelled. Similarly, the behavior is not proof that a cat has detected something dangerous or that it can smell every substance better than a person.

Other behaviors can look vaguely similar. A cat may open its mouth while vocalizing, grooming, eating, or investigating an object. Context matters: flehmen usually follows focused sniffing and consists of a short, still pause. Repeated gulping, drooling, coughing, or visible effort to breathe is not the usual pattern.

When the behavior is ordinary—and when to call a vet

A relaxed cat that briefly opens its mouth after investigating a smell and then returns to normal is usually showing a normal behavior. There is generally no need to interrupt it or put an object near the cat’s nose to provoke the response. Let the animal investigate voluntarily, and avoid forcing it to smell substances.

Contact a veterinarian if open-mouth breathing happens at rest, persists, or comes with signs such as labored or unusually rapid breathing, weakness, collapse, marked distress, or a change in normal behavior. Also call a veterinarian if the mouth stays open or the cat seems unable to close it, or if there is repeated drooling, gagging, or difficulty eating. These signs have causes that cannot be identified reliably from the posture alone; a veterinarian can assess the cat. Do not assume that every open mouth is a harmless scent response.

Strong household chemicals, smoke, and other irritating fumes should not be offered as “interesting smells.” Keep cats away from potentially harmful substances and follow product safety instructions. The flehmen response is a natural behavior, but it is not a reason to expose a pet to an unknown or irritating scent.

Frequently Asked Questions

Why does my cat make a funny face after smelling something?

The raised lip and parted mouth are often the flehmen response. The cat is directing scent cues toward the vomeronasal organ for closer chemical investigation; it is not necessarily expressing disgust.

Are cats tasting smells when they open their mouths?

Not in the everyday sense of tasting food. They are using a specialized sensory route associated with the vomeronasal organ to examine chemical cues.

Why does my cat do this after sniffing another cat’s urine?

Urine can contain chemical signals that cats investigate through smell and the vomeronasal system. The response helps examine the scent, but the exact information the cat detects cannot be read from its expression.

Is it normal for a cat to breathe with its mouth open?

A brief open-mouth pause immediately after sniffing may be flehmen. Ongoing panting or open-mouth breathing, especially at rest or with visible effort, is different; call a veterinarian.

Do all cats show the flehmen response?

No. Cats vary in whether and how noticeably they show it, and the response depends on the scent and situation. Not seeing it does not mean a cat cannot detect chemical cues.

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.