Direct answer: When a cat pauses over a smell, opens the mouth slightly, curls the upper lip, and seems to stare, the cat may be performing the flehmen response. This behavior helps move scent molecules toward a specialized sensory organ in the roof of the mouth. It is usually scent investigation, not a silent meow, disgust, or proof that the cat is upset. Log what the cat smelled, how long the response lasted, and what happened next before interpreting the scene.
A newly published Current Biology study identified stable, individual differences in branched-chain fatty acids in domestic-cat urine. In controlled tests, cats could discriminate donor-specific mixtures, suggesting that some scent marks may carry information about which cat left them. The finding does not mean owners can decode a particular cat’s chemical message at home, and it does not make every open-mouth expression a flehmen response.
Use the free AI Pet Translator to organize a description of the sound, posture, location, scent source, and sequence. Its output is an interpretation for entertainment and daily-care reference, not a literal translation or diagnosis.
What a flehmen response can look like
The expression is often brief: the cat stops sniffing, holds the mouth partly open, may lift the head, and appears to freeze for a moment. The surrounding sequence matters more than the face alone.
| Observed scene | Useful context to record | Cautious interpretation | Next step |
|---|---|---|---|
| Brief open-mouth pause after sniffing a new object | Object source, duration, ears, tail, and whether the cat resumes normal activity | May be scent investigation | Allow space and observe without interrupting |
| Open-mouth pause near a doorway or window after another cat passed | Presence of outdoor cats, recent visitors, new packages, and repeat visits to the spot | May reflect interest in unfamiliar animal scent | Reduce unwanted visual or scent triggers if the cat remains unsettled |
| Tail quiver and a small amount of urine on a vertical surface | Location, household changes, outdoor cats, frequency, and posture | More consistent with urine marking than ordinary toileting | Do not punish; document the pattern and discuss persistent indoor marking with a veterinarian |
| Repeated mouth opening away from any obvious smell | Breathing effort, drooling, appetite, energy, and gum color | Do not assume it is flehmen | Seek veterinary guidance, urgently if breathing is difficult |
| Frequent litter-box visits or straining | Urine output, vocalization, licking, posture, and time since normal urination | May be a health concern rather than communication | Contact a veterinarian promptly; inability to pass urine is an emergency |
The SCENT context log
Record one event at a time with the five-part SCENT log:
- S – Source: What was the cat smelling: another cat’s area, shoes, a package, bedding, the litter box, or an unknown spot?
- C – Cat posture: Note mouth position, head height, ears, tail, pupils, crouching, and muscle tension without assigning an emotion yet.
- E – Event before: Record arrivals, cleaning, a window encounter, household change, toileting, play, eating, or another cat’s movement.
- N – Next action: Did the cat walk away, rub, scratch, spray, hide, investigate again, eat, play, or rest?
- T – Time and repetition: Add duration, time of day, location, and whether the same sequence repeats.
A useful entry is factual: “10:15 a.m.; sniffed visitor’s shoe; mouth open for four seconds; ears neutral; walked away and groomed.” A weak entry jumps to a conclusion: “The shoe smell made her jealous.” Facts can be compared across days; labels cannot.
What the new research does and does not show
Verified finding
The 2026 study found individually distinctive BFA profiles in cat urine that were relatively stable within a cat. Behavioral tests indicated that cats discriminated different donor-derived BFA compositions. The researchers linked these compounds to lipid droplets in the kidney that may help buffer short-term variation.
Cautious interpretation
A cat’s flehmen response can be treated as evidence that the cat is analyzing an interesting scent. In a real home, however, the owner usually does not know which molecules triggered the response or what information the cat obtained. The cat may be sampling urine-related compounds, other pheromones, or simply a strong unfamiliar odor.
What is not established
The study does not provide a home test for identifying the donor, does not show that every urine mark has one fixed “meaning,” and does not support translating scent into human sentences. It also does not turn sudden indoor urination into a harmless communication issue; medical causes still need to be ruled out.
A one-minute observation workflow
- Do not move the object or call the cat during the first few seconds.
- Observe the face and whole body together.
- Identify the likely scent source without bringing it closer to the cat.
- Record the action immediately before and after the expression.
- Check whether the cat returns to normal activity.
- Compare at least three similar events before suggesting a pattern.
If the event occurs near the litter box, compare it with the cat meowing near the litter box context log. For interaction-specific observations, the stop-or-continue cat play log shows how to separate an observed pause from an assumed emotion.
Keep scent investigation separate from spraying
Flehmen is an information-gathering behavior. Urine spraying is scent deposition. A spraying cat commonly stands, backs toward a vertical surface, raises or quivers the tail, and releases a small amount of urine. Ordinary toileting usually involves squatting and a larger amount of urine on a horizontal substrate. These patterns can overlap with stress or health issues, so an observation log should support professional assessment rather than replace it.
Never punish a cat for spraying or unusual toileting. Punishment can increase fear and hides the context needed to solve the problem. Clean affected areas with a cat-safe enzymatic product and avoid ammonia- or bleach-based cleaners around cats.
Optional daily-care tool
If access or box height is part of the scene, the Open Low-Front Cat Litter Box with Scoop is an optional routine-care product to review. A different box does not diagnose or treat spraying, straining, pain, or repeated inappropriate urination; those concerns require veterinary guidance.
When to stop logging and call a veterinarian
Contact a veterinarian for a sudden change in toileting, repeated urination outside the box, blood in urine, pain, reduced appetite, vomiting, marked lethargy, persistent drooling, or repeated open-mouth behavior without a clear scent trigger. Straining with little or no urine, collapse, blue or pale gums, or open-mouth breathing can be urgent emergencies.
Frequently asked questions
Why does my cat open its mouth after smelling something?
The cat may be using the flehmen response to direct scent molecules toward the vomeronasal organ. Record the scent source and the next action rather than assuming one emotion.
Is the flehmen response the same as a silent meow?
No. A silent meow is a vocal gesture with little or no audible sound, often directed toward a person. Flehmen usually follows sniffing and functions as scent investigation.
Does flehmen mean my cat smells another cat?
It can occur around animal scent, including urine-related cues, but it may also follow other strong or unfamiliar smells. The expression alone cannot identify the source.
Should I stop my cat from making the flehmen face?
Usually no. If the cat is otherwise comfortable, allow a brief investigation. Remove access only when the substance itself may be unsafe or the cat becomes distressed.
Can an AI pet translator decode cat scent messages?
No. It can help organize observations and suggest cautious possibilities from the context you provide, but it cannot chemically analyze scent or translate it into exact language.
Sources and context
- Current Biology: “Signatures of branched-chain fatty acids derived from a kidney reservoir confer stable chemical individuality on domestic cats”, online article August 19, 2026; issue publication September 7, 2026. Primary evidence for stable individual BFA profiles and behavioral discrimination.
- ScienceDaily: “Scientists discover a hidden ‘ID card’ in cat urine”, September 20, 2026. Current public-interest signal that prompted this context guide; factual claims were checked against the primary paper.
- Cats Protection: “How do cats communicate with each other?”, published January 2026. Practical explanation of scent communication and the flehmen response.
- VCA Animal Hospitals: “Cat Behavior Problems: Marking and Spraying Behavior”, accessed September 21, 2026; the page does not display a publication date. Veterinary-reviewed distinction between spraying, toileting, context, and health concerns.
This guide is for entertainment and general daily-care reference. It does not provide a diagnosis, guarantee an interpretation, or replace veterinary or qualified behavior advice.