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Cats are usually such graceful and delicate creatures, so it can come as a real surprise when they suddenly lean over to a fellow cat and get a good whiff of their rear. Why do cats do this?

It seems pretty weird, especially considering how humans communicate, but it’s actually an important part of feline behavior. Here’s why.

Butt sniffing is a very natural, instinctual, and basic form of cat-to-cat communication. Strangely enough, it is how cats greet and get to know each other, along with sniffing of the chest and neck. Even cats that know each other well will sniff butts to “see what’s new” and reinforce their bond and communication.

The cat butt sniff is the feline equivalent of “Hello, how do you do?” and similar to how humans use a handshake when meeting and being introduced to someone. Cats communicate with each other using their strong sense of smell and detect signals in the chemicals in oil from the anal glands.

What a Sniff Can Reveal

To understand what a sniff can tell a cat, it is important to understand how cats are different. There are four main differences between the way cats communicate and humans communication:

• The first difference between cats and humans is a cat’s amazing sense of smell. They are reported to have approximately 40 times more smell-sensing cells in their nasal passages than we do. With such a super ability to smell, cats rely on this sensory information far more than humans. It’s so strong that a cat entering a room can perceive if another cat previously in the room was happy, stressed, scared, or in heat. Although it is difficult for humans to completely understand exactly how this works, the “sniff” can somehow also tell the cats if the encounter is likely to be friendly or not friendly.
• Cats have prominent and active scent glands on their head, neck, paws, chest, and base of the tail, as well as active anal glands. These apocrine glands, which sit on each side of a cat’s rectum, produce strong-smelling secretions intended to send chemical signals about that cat’s identity to other animals. These signals include information like the sex of the cat, what the cat is eating, and even some clues about a cat’s emotional state.
• The third difference of note is the presence of the Jacobson’s organ (also known as the vomeronasal organ). This is a small piece of olfactory nerve tissue filled with extrasensory receptors that perceive odors transmitted through the air. Also present in many animals including dogs, snakes, and even elephants, it transmits information to the brain from its position just inside the nose and mouth. You might notice a cat is activating their Jacobson’s organ when they make a funny face called the “Flehman response.” Cats will often tilt their nose up and curl their lip to optimize their ability to “smell” in this way.
• The last big difference is that unlike humans, cats will reintroduce themselves frequently, sometimes several times in a day or even an hour. Any change or stimulus will often lead to the butt sniff. Some believe the “sniff” can actually relieve tension and stress by helping an individual feel more comfortable about the other cat. Two cats living in the same house may smell each other when one comes in from the outside or comes back from the vet to confirm information about the cat’s state including diet, stress, availability for mating, and mood.

What You Should Do During Butt Sniffing

Behaviorists suggest that because the butt sniffing routine is a normal part of cat behavior, it’s best not to interrupt it if the cats seem friendly. Interrupting this behavior is equivalent to you stopping a friend from shaking hands with someone they are meeting: it can annoy or upset the friend and can make the introduction awkward. In fact, lack of this butt sniffing communication between cats can create stress between the cats.

With that being said, some cats are more aggressive “sniffers” than others and not every cat that meets will actually like each other. If the sniffing gets intense and you notice any other signs of aggression, then it is appropriate to pull your cat away from the other.