The Flehmen Response

Why Your Cat Pulls That Face

Every so often a cat will sniff at something — another cat's scent, a patch of urine, your shoe, a new object — then freeze with its mouth hanging half-open, upper lip curled back, and a fixed, faintly appalled expression. This is the flehmen response (from a German word meaning to curl the lip), and far from being revulsion, it is one of the most sophisticated things a cat's face ever does.

A Second Sense of Smell

Cats possess a structure most people never hear about: the vomeronasal organ, also called Jacobson's organ, a small pouch of scent-detecting tissue in the roof of the mouth that connects to the mouth via two tiny ducts just behind the front teeth. It sits between the senses of smell and taste and is specialised for detecting pheromones — the chemical signals cats use to communicate about identity, territory, and reproductive status.

To use it, the cat has to physically route scent particles onto the organ. That is exactly what the open-mouthed grimace does: by holding the mouth ajar and pressing the tongue against the roof of the mouth, the cat channels scent molecules up into Jacobson's organ, effectively tasting the smell to read the fine detail an ordinary sniff would miss.

What It Means for You

The flehmen response is completely normal and healthy — a sign of a curious, investigating cat. You are most likely to see it around:

• The scent of another cat, especially urine marks or spots where a cat has rubbed
• Interesting human scents — sweaty socks, shoes, or skin
• New objects or visitors brought into the home
• Reproductive scents, which is why unneutered toms flehmen so dramatically

There is nothing to correct or discourage. It simply means your cat has found something worth analysing in depth. Horses, big cats, and many other mammals do exactly the same thing.

When to Be Concerned

Flehmen itself is never a problem. However, if a cat holds its mouth open persistently outside of scent-investigation — panting, drooling, pawing at the mouth, or showing distress — that is a different matter and may indicate dental pain, nausea, a foreign object, or breathing trouble, and warrants a vet check.