That open-mouthed stare after sniffing a spot of urine is not a yawn and not a grimace. It is flehmen, a 0.5–2 second gape that pulls air across a second scent organ sitting behind the upper front teeth. The system reads chemical signals the ordinary nose cannot: who passed by, what sex they were, how recently, and whether they are worth answering. Intact males run the behaviour 3–5 times more often than queens, and a cat that never does it is usually normal, not ill.
What the 0.5–2 second gape looks like
The sequence runs in 3 steps. The cat sniffs the spot for 2–4 seconds at 5–30 cm, lips parted. Then the head lifts, the mouth opens 1–2 cm, the upper lip curls back, and the nose wrinkles; the tongue stays in. The mouth holds that position 0.5–2 seconds, sometimes 3, then closes and the cat swallows once. The ears stay forward and the body stays loose.
Contrast that with pain: a cat with a sore mouth holds the jaw open for 5–20 seconds, drools, paws at the muzzle, and stops eating for 24 hours or more. Flehmen is a 2-second event repeated 2–4 times at one site. A gape that lasts longer than 5 seconds, comes with 3 or more swallows, or appears without any scent source is a different problem.
2 scent systems, 2 different jobs
The main olfactory system lines the nasal cavity and reports odour: what something smells like. Cats carry roughly 200 million receptor cells there, against about 5–6 million in people, so a 1:1000 dilution of a scent still registers.
The vomeronasal organ (VNO) is separate. It is a paired, tube-like structure about 1 cm long, sitting on either side of the nasal septum and opening through 2 narrow ducts, roughly 1 mm across, just behind the upper incisors. It does not report odour. It reports chemical messages, and its nerve fibres run to the amygdala and hypothalamus, the parts of the brain tied to arousal, marking, and social response. Air reaches it by a different route: not through the nostrils, but pumped up from the mouth when the palate lifts during the gape.
What the gape is sampling
In practice, the triggers are body fluids and gland secretions rather than food. Urine, especially sprayed urine on a vertical surface, is the classic. Cheek-gland rubbing on a door frame, anal-sac fluid, interdigital glands between the toes, and the chin glands all carry the same kind of signal, which is why cats gape after sniffing a spot another cat rubbed 2–3 days earlier. The glands between the toes sit in the same family, and their layout is covered in claw and paw anatomy.
Distance and repetition matter. Most cats sample at 5–30 cm, take 2–4 pulls at one site, and move on. A cat that repeats the gape 5 or more times at the same 10 cm patch is usually reading a fresh mark from an unfamiliar animal, and the follow-up is often spraying, chin rubbing, or a 30–60 second stand-and-stare at the spot.
Why toms gape 3–5 times more
The behaviour is testosterone-dependent. Intact males start showing it around 4–6 months, peak between 1 and 5 years, and use it during patrol: sample, gape, then mark within 1–2 minutes roughly 1 time in 3. Queens show it too, most often in the 3–7 days around estrus, and they tend to gape at male urine rather than at their own. Neutered males sit in between and often keep a reduced version of the habit, which is why a desexed 6-year-old tom still gapes at the door frame.
Owners read this as disgust at a bad smell. The opposite is closer: the gape is the collecting motion, and it usually means the cat found something worth analysing, whether that is urine or a visitor's shoe.
5 scent sources and typical response
| Source | Gapes per 10 min | Hold time (s) | Most likely to gape |
|---|---|---|---|
| Sprayed urine, intact male | 3–5 | 1–2 | Intact male |
| Cheek-gland rub on frame | 2–4 | 0.5–1.5 | Either sex |
| Estrus urine | 4–6 | 1–2 | Intact male |
| Anal-sac fluid on bedding | 2–3 | 0.5–1 | Either sex |
| New object or visitor's shoe | 1–2 | 0.5–1 | Curious adults |
The pattern in that table is the useful part: 1–2 gapes at a novel object is curiosity, 4–6 at urine is a social read, and 5 or more at the same spot twice in 10 minutes usually predicts marking within the hour.
When a gape is not flehmen
Take the cat to a vet if the mouth stays open for more than 5 seconds, if there is drooling, a dropped jaw, or a 1-sided swelling under the eye, or if food intake falls by half for 2 days. Dental disease, a foreign body under the tongue, and upper respiratory infection all produce a gaping cat, and none of them involve the VNO. Cats hide mouth pain well, so a 10% drop in intake over 5 days is already a signal, and a cat that stops grooming for 48 hours is worth an exam. If intake falls without any mouth sign, compare stool timing against digestive transit before assuming the problem is dental.
Reading it at home in 15 minutes
You can test the response without equipment. Put 1 drop of urine from another cat on a cotton swab, hold it 10 cm from the nose for 5 seconds, and count gapes for 2 minutes. Wait 5 minutes, then repeat at 20 cm and again at 30 cm. Most cats gape at 10 cm and stop responding by 30 cm, which maps the working range. Do 1 trial per day for 3 days rather than 3 in a row: repetition at 2-minute intervals shuts the response down for 30–60 minutes.
Record 2 things: whether a gape happened and how long it lasted. A cat that gapes within 3 seconds is simply more responsive, which tracks interest more than health. For age effects, the cat age calculator puts a 7-year-old at roughly 44 human years, where scent interest often flattens.
What the organ does not do
It is not a disease detector and it does not make a cat a better sniffer. A cat with a blocked VNO duct still eats, plays, and finds food; the deficit shows up in social signalling, not appetite. Claims that the organ can be trained, or that gaping proves a cat loves one person, have no support. Read it as data collection, 0.5–2 seconds at a time.
4 things to watch this month
- Count gapes at 1 familiar spot and 1 new object: 2–4 is typical, 6 or more means a fresh mark.
- Time the hold: 0.5–2 seconds is normal, over 5 seconds is a mouth problem.
- Note who gapes in a multi-cat house; 1 cat doing most of it is often the intact male.
- Track food intake for 5 days if gaping appears alongside drooling or a dropped jaw.
Terms mentioned in this article
Frequently asked
Is the open mouth after sniffing a sign of disgust?
No. It is a collecting motion called flehmen, held for 0.5 to 2 seconds, that pushes air across the vomeronasal organ behind the upper incisors. The organ sends signals to the amygdala and hypothalamus rather than the cortex, so the cat is reading social information such as sex, identity, and how fresh a mark is.
Why does my neutered male still do flehmen?
The behaviour depends on testosterone but does not vanish with neutering. Intact males gape 3 to 5 times more often than queens and peak between 1 and 5 years, while neutered males usually keep a reduced version. A 6 year old desexed tom gaping at a door frame is normal, and it is not a health sign on its own.
When does an open mouth mean a vet visit?
Go if the mouth stays open longer than 5 seconds, if there is drooling, a dropped jaw, or one sided swelling under an eye, or if food intake falls by half over 2 days. Dental disease, a foreign body under the tongue, and upper respiratory infection all cause gaping without involving the vomeronasal organ.