Cats open their mouths after smelling something because they’re doing a special “extra‑smelling” move called the flehmen response, which sends scent particles to a second smell organ on the roof of the mouth for deeper analysis. It’s normal, often looks like a funny “stink face,” and is usually triggered by interesting odors such as other animals’ scents or strong environmental smells.

What’s Actually Happening

  • When your cat smells something intriguing, they may pause, open their mouth slightly, and curl their lips back in a weird-looking grimace.
  • This expression helps draw scent molecules into a specialized structure called the vomeronasal (Jacobson’s) organ, located just behind the upper front teeth on the roof of the mouth.

The Flehmen Response Explained

  • The flehmen response is like “smelling in HD,” combining aspects of smelling and tasting so the cat can read pheromones and other complex chemical signals more precisely.
  • Tiny ducts just behind the incisors allow air and scent particles from the mouth to reach this organ, giving the cat more detailed information than the nose alone can provide.

Why Cats Do It

  • This behavior helps cats gather social and environmental information, such as other cats’ territories, reproductive status, and the presence of unfamiliar animals.
  • It is most commonly triggered by urine marks, other cats’ scent glands, new objects, or any unusual or particularly strong smell around the home or outdoors.

Is It Normal Or A Problem?

  • In the context of sniffing something then holding the mouth open briefly, it is considered a normal, healthy reflex and not a sign of illness.
  • However, if a cat is panting, breathing with mouth open for long periods, drooling heavily, or seems distressed, that can indicate medical issues such as respiratory problems, heat stress, or toxin exposure and warrants a vet visit.

Fun Extra Facts

  • Many mammals show a flehmen response, including big cats, horses, giraffes, rhinos, and others, not just house cats.
  • To humans it looks like a silly “stink face,” but to a cat it is a serious information-gathering tool that helps them navigate their social world and environment.

Information gathered from public forums or data available on the internet and portrayed here.