Why does a cat hold its mouth open after smelling something?
The flehmen response draws scent chemicals toward the vomeronasal organ in the roof of the mouth.
Topic illustration selected for this guide. Some learning images may be AI-assisted.Why does a cat hold its mouth open after smelling something — the quick answer
✓ The flehmen response draws scent chemicals toward the vomeronasal organ in the roof of the mouth.
✓ Let the cat finish investigating and clean marked areas with an appropriate enzyme cleaner when needed.
✓ Open-mouth breathing rather than a brief scent response is an emergency.
The flehmen response draws scent chemicals toward the vomeronasal organ in the roof of the mouth. It often follows investigation of another animal's scent and can look like a surprised grimace. Here is the useful version of the answer: what the behaviour may mean, what it does not prove and when it stops being just a fun cat fact.
The short answer
The flehmen response draws scent chemicals toward the vomeronasal organ in the roof of the mouth. A single moment never tells the whole story, so compare the setting, the cat's posture and what happens next.
Why cats do this
It often follows investigation of another animal's scent and can look like a surprised grimace. Cats combine scent, sound, sight, touch, memory and learning. That is why the same visible action can have more than one reasonable explanation.
Read the whole cat
Look at ear direction, pupils in the current light, tail movement, muscle tension, distance and freedom to leave. Relaxed behaviour is loose and changeable; concern is more likely when the body stays tense, the cat cannot disengage or normal routines change.
What to do at home
Let the cat finish investigating and clean marked areas with an appropriate enzyme cleaner when needed. Avoid forcing a repeat for a photo or testing a viral claim. The most cat-friendly response gives choice, protects safety and rewards calm alternatives.
What this does not prove
This behaviour does not prove that every cat feels the same emotion or shares a human intention. Personality labels can be fun, but age, health, experience, environment and reinforcement explain much more than coat colour, sex or a single gesture.
When to contact a veterinarian
Open-mouth breathing rather than a brief scent response is an emergency. Seek faster help for breathing difficulty, collapse, seizures, major trauma, suspected poisoning, severe pain or repeated unsuccessful attempts to urinate.
Your quick checklist
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Three simple things you can do
You do not have to change everything today. Pick one step that feels realistic, try it and see how your cat responds.
- 1Let a brief scent investigation finish without touching the cat's face or mouth.
- 2Note the trigger and confirm that breathing immediately returns to quiet closed-mouth breathing.
- 3Call emergency care for open-mouth breathing, breathing effort, blue or pale gums, weakness or collapse.
Common mistakes
×Calling every open mouth a harmless flehmen response.
×Holding an unfamiliar scent closer to repeat the expression for a photo.
×Waiting on open-mouth breathing because the cat recently smelled something.
Questions cat people ask
Why does my cat make a funny face after sniffing?+
During the flehmen response, a cat briefly holds the mouth open to move scent compounds toward the vomeronasal organ. It often follows investigation of another animal's scent.
How do I distinguish flehmen from breathing trouble?+
Flehmen is brief, tied to sniffing and not accompanied by respiratory effort. Continued open-mouth breathing, abdominal effort, distress or abnormal gum colour is an emergency.
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Checked, dated and transparent
- Prepared by
- EverYes Cats editorial team
- Last updated
- 8 August 2026
- Source checked
- 8 August 2026
- Primary reference
- Merck Veterinary Manual ↗
We begin with the named reference, rewrite the information in plain language and add practical cat-parent steps. Urgent health statements are checked against veterinary sources. This guide has not been individually reviewed by a veterinarian unless explicitly stated. It provides education, not diagnosis or treatment.
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Your head is warm, relatively still and carries a strongly familiar scent.