Cats open their mouths after smelling something because they’re using a special “extra” smelling system called the flehmen response, which sends scent particles to a sensory organ on the roof of the mouth for a kind of smell‑plus‑taste analysis. It looks funny or dazed, but it’s normal and helps them read pheromones and other important chemical signals from their environment.

What’s Actually Happening?

  • When your cat sniffs, then freezes with its mouth slightly open, lips a bit curled, that is the flehmen response.
  • This posture pulls scent‑laden air into the vomeronasal (Jacobson’s) organ, a special sensor located in the roof of the mouth just behind the front teeth.
  • The organ “reads” pheromones and other complex chemical cues, giving the cat richer information than normal nose‑smelling alone.

You can think of it like your cat switching from “regular definition” to “HD” smell mode.

Why Do Cats Need This?

  • Cats are highly scent‑driven animals; chemical messages help them understand territory, mating status, stress, and identity of other animals.
  • The flehmen response is especially useful for decoding pheromones in urine marks, other cats’ scent glands, or new/strong smells in the home.
  • This behavior is common in many mammals, including lions, horses, giraffes, and others, so your pet is doing a very ancient, normal animal thing.

When You’ll See That “Stink Face”

You’re most likely to notice the open‑mouth smell when your cat encounters:

  • Another cat’s urine, feces, or scent marks (on scratching posts, bedding, or your clothes).
  • New pets, new humans, or strange outdoor smells brought in on shoes or bags.
  • Intense or unusual odors like certain foods, catnip, or areas another animal recently rubbed or sprayed.

The expression can look like:

  • Mouth slightly open, sometimes tongue touching the roof of the mouth.
  • Eyes half‑closed or “far away,” almost like they’re in a trance.
  • A short freeze, then they resume normal activity.

All of that is expected and healthy behavior.

When Is It NOT Normal?

Most of the time, this is nothing to worry about, but consider a vet visit if you notice:

  1. Mouth held open often or for long periods
    • If your cat breathes with its mouth open regularly, especially when resting, this can signal respiratory distress, heart issues, or pain, which is very different from the brief flehmen face.
  1. Other worrying signs with it
    • Drooling, pawing at the mouth, foul odor, visible sores, or difficulty eating could suggest dental or oral problems.
 * Repeated gagging, coughing, or labored breathing should be treated as urgent.

If it’s just an occasional weird face after a sniff, it’s almost certainly normal; if it’s frequent, prolonged, or paired with distress, a professional exam is the safest move.

Quick Scoop Summary

  • The open‑mouth “after smelling” look is the flehmen response , not your cat being confused or disgusted.
  • It channels scent molecules to the vomeronasal (Jacobson’s) organ for advanced processing of pheromones and complex smells.
  • It’s normal, seen in many species, and usually nothing to worry about unless it’s constant, paired with heavy breathing, or other signs of illness.

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