Why Does My Cat Make That Weird "Stink Face"? The Flehmen Response Explained

You've almost certainly seen it. Your cat leans in to investigate your shoe, another cat's spot on the sofa, or a patch of carpet — and then everything stops. The mouth drops half-open, the upper lip curls back to bare the front teeth, the eyes glaze slightly, and your cat holds this frozen, faintly appalled expression for a few seconds as if it has just caught a whiff of something truly offensive. Cat owners have nicknamed it the "stink face" or "sneer," and the natural assumption is that the cat smelled something disgusting. In fact it's the opposite: your cat has found a smell so interesting that a normal sniff wasn't enough. What you're watching is the flehmen response, and it's one of the most remarkable pieces of equipment your cat owns.

Jackson Galaxy breaks down exactly what your cat is doing when it pulls the "stinkface."

Your Cat Has a Second Nose

The flehmen response exists because cats — like horses, big cats, and many other mammals — have a specialised scent organ that we humans functionally lack. Tucked into the roof of the mouth, just behind the upper incisors, sit two tiny openings that lead to the vomeronasal organ, also called Jacobson's organ. Think of it as a second nose, but one tuned to a very particular job: detecting pheromones and other heavy, non-volatile chemical signals that ordinary nostril-sniffing can't fully process.

When your cat curls its lip and holds its mouth open, it isn't grimacing — it's actively pumping scent molecules up toward those openings. The stalled, trance-like expression keeps the mouth in exactly the right position long enough for the vomeronasal organ to draw the scent in and route it to the brain. In effect, your cat has stopped smelling in standard definition and switched into a kind of chemical super-resolution.

What Cats Are Actually "Tasting"

The vomeronasal organ specialises in the social and biological chemistry of other animals. When a cat performs flehmen, it's usually gathering information such as:

• Reproductive status. Intact males and females use it to read the hormonal signals in urine and scent marks — who is in heat, who has passed through, who's available.
• Identity and territory. The organ helps decode the individual "signature" of another cat, the boundaries they've marked, and how recently they were around.
• Emotional and pheromone cues. Cats leave behind chemical messages from glands on their cheeks, paws, and flanks. Flehmen helps a cat read those messages in full.
• Novel, complex smells. Sometimes the trigger is simply something unfamiliar and rich — your sweaty gym socks, a guest's shoes, bleach, or another pet's bedding.

This is why the behaviour is often centred on urine, other cats' scent marks, and — a little awkwardly — parts of you that carry strong scent. Your cat isn't judging your hygiene. It's reading a dense chemical story, and its face just happens to look like a critic mid-review.

How to Recognise It (and Tell It From Trouble)

A genuine flehmen response has a very specific, unmistakable pattern once you know it:

• The cat investigates a scent closely, often after a deliberate sniff.
• The mouth opens partway and the upper lip pulls up, exposing the front teeth.
• The cat goes still, almost statue-like, sometimes with a slightly wrinkled nose and unfocused eyes.
• The whole thing lasts a few seconds, then the cat relaxes and carries on as if nothing happened.

Crucially, flehmen is calm and self-contained. That's what separates it from things that actually need attention. If your cat is pawing at its mouth, drooling heavily, gulping or swallowing repeatedly, sneezing in fits, or looks genuinely distressed, that's not flehmen — that could be a dental problem, nausea, or something stuck in the mouth, and it's worth a look and possibly a vet call. The flehmen sneer, by contrast, leaves the cat perfectly content the moment it's finished.

A wider look at just how powerful — and strange — your cat's sense of smell really is.

Just How Good Is a Cat's Nose?

To appreciate the flehmen response, it helps to appreciate the whole system it belongs to. A cat's sense of smell utterly dwarfs ours. Humans have roughly 5 million scent receptors in the nose; cats have on the order of 45 to 80 million. The vomeronasal organ adds a second, dedicated channel on top of that ordinary smelling power — one specialised for exactly the kind of social chemistry that matters most to a territorial, scent-driven animal.

This is a big reason cats experience the world so differently from us. Scent is their primary social currency. They greet by smell, map their territory by smell, assess strangers by smell, and soothe themselves with the familiar smells of home. The flehmen response is the moment you actually get to see that hidden sense working — the visible tip of an enormous sensory iceberg.

Do All Cats Do It? And Should You Worry?

Every healthy cat has a functioning vomeronasal organ, but some show the flehmen response far more openly than others. Unneutered cats — and cats living in multi-cat or outdoor environments where scent politics run hot — tend to flehmen more often, because there's simply more pheromone information worth investigating. A neutered indoor cat may do it only occasionally, when it stumbles on something unusually interesting. Kittens can display it too, sometimes looking especially comical as they figure out their own equipment.

Here's the reassuring bottom line: the flehmen response is completely normal, healthy, and nothing to correct. It is not a sign of illness, disgust, aggression, or distress. You never need to intervene, and there's no need to change anything about your cat's environment because of it. If anything, it's a small privilege — a rare, visible glimpse into a sensory world far richer than our own.

The Takeaway

Next time your cat freezes mid-sniff and pulls that wide-eyed, open-mouthed "stink face," resist the urge to feel insulted. Your cat hasn't found something revolting — it has found something fascinating, and it's cranking its sense of smell up to maximum resolution to read every detail. That funny grimace is your cat quietly using a superpower you'll never have. Enjoy the show.

This article is general information, not veterinary advice. The flehmen response itself is normal, but if your cat is pawing at its mouth, drooling, retching, or seems unwell, contact your veterinarian.