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If you’re a cat person, like me, you’ve probably seen your furry friend looking... disgusted with you..? There’s this face they make, like with the wrinkled up nose, curled back lip, and the open mouth, that looks like they’re just absolutely revolted.

Good news, your cat doesn't actually think you’re gross. Or, if they do, that face isn’t how they show it. That sneer is actually what’s known as the Flehmen response, and it gives cats and other animals, like horses, llamas, dogs, and giraffes a supercharged way to smell the environment around them.

While it might look like cat are expressing their distaste, what they’re actually doing with that face is “sniffing” using a specialized organ called the vomeronasal organ. It sits kind of underneath the nose in the roof of the mouth. And it’s actually connected to the mouth by small, fluid-filled ducts called nasopalatine canals.

If you look in your cat’s mouth, you can even see the ends of these, they’re behind the sharp incisors. Though, good luck getting them to sit still while you like, take a look at the inside of its mouth. Anyway, because of the fluid in these ducts, scents don’t passively drift up there.

So to “sniff”, airborne scents have to be taken in through the mouth, dissolved in fluid, and then pumped up until they come into contact with the organ’s sensory cells. And that is where that funny face comes in. When a cat, or giraffe, or horse pulls back their lips into the grimace of the Flehmen response, they’re opening up those canals and starting the pumping action to take a deeper whiff.

They could just rely on their nose, but the vomeronasal organ has its own set of chemical receptors, so it can smell different smells. This system is primarily used to detect scent signals from members of their own species, though different animals, and even different sexes of the same animal, can use this secondary smelling system in different ways. And that might explain why people tend to associate the flehmen face with cats and horses more than with dogs, even though all of them can sniff this way.

In case you’re wondering though, you cannot. Humans lost all of those nasopalatine ducts a long time ago. And while there are some remnant cavities where your vomeronasal organs once were, it’s been awhile since they could detect anything.

Which is all to say: don’t worry if your cats are making weird faces at you. They don’t hate you. But… they might think you smell.

Thanks for asking, Paul G.! And thanks to all of our patrons on Patreon who voted in our poll. If you want the chance to vote on which questions we answer, or get some really awesome rewards, you can learn all about the perks of being one of our patrons at Patreon.com/SciShow. [ ♪ Outro ].