Why Cats Sniff Rear Ends

There is no delicate way to ask. This issue is as sensitive as a cat’s sense of smell. To address why cats sniff rear ends, it is important to understand their sense of smell and their communication techniques.

Do cats really have a good sense of smell?

Like humans, cats have five basic senses: taste, touch, hearing, sight, and smell. Of these senses, smell takes the lead in the feline world. A cat's sense of smell is far more advanced than ours. When compared to humans, cats have a smelling ability that is 14 times more sensitive. The human nose contains about 5 million olfactory receptors that detect aromas, while a cat's nose has 45 to 80 (possibly up to 200) million scent receptors.

Plus, cats have an additional tool to enhance their sense of smell. Cats have a special organ called Jacobson’s organ (also known as the vomeronasal organ), which is located inside the nasal cavity and opens into the roof of the mouth, right behind the upper incisors. This amazing organ serves as a secondary olfactory system and detects specific chemicals by using nerves that lead directly to the brain. Unlike olfactory cells in the nose, the odor receptors in Jacobson’s organ do not respond to ordinary smells. In fact, these nerve cells respond to a range of substances that often have no odor at all; they work to detect “undetectable” odors.

"Kittens can identify their mother from other cats using their sense of smell."

Jacobson’s organ communicates with the part of the brain that deals with mating. By identifying pheromones, Jacobson’s organ provides male and female cats with the information they need to determine if a member of the opposite sex is available for mating. In addition, this organ enhances the sense of smell that newborn kittens need to find their mother’s milk. Kittens can identify their mother from other cats using their sense of smell. Kittens placed between two nursing mothers will move to the one that gave birth to them.

The two separate parts of the cat’s odor detection system, the nose and Jacobson’s organ, work together to provide delicate sensibilities that neither system could achieve alone. When a cat curls her lips and appears to smile, she opens up Jacobsen’s organ, and air pushes smells into it.

Do cats use smell to communicate?

When two people meet, they evaluate body language, facial expressions, and tone of voice to quickly assess each other. With this information, they may choose to shake hands or hug each other, share a casual verbal greeting, cry with joy, or totally ignore each other.

Cats may not verbalize, shake hands, or hug like humans, but they do assess each other. When two cats meet, they usually sniff the head area first or may even share a gentle head bump. This physical greeting releases pheromones from glands in the face. These pheromones tell a lot about a cat, so a cat's sense of smell serves as a form of chemical communication.

Biochemical compounds emitted by cats are a mode of chemical communication. The aromas tell a cat what her new-found friend likes to eat and what sort of mood she is in. By simply smelling a companion, a cat can determine whether they are male or female, happy or aggressive, healthy or ill. Cats can get a general idea about each other with a quick sniff of the head, and can get more detailed information by getting up close and personal.

So why do cats smell each other’s rear ends?

What perplexes many pet owners is why cats sniff this particular part of the anatomy. Why rear ends? Why not ears or feet? The answer is anatomical. Inside the rectum are two small sacs called anal glands, which secrete a noxious-smelling substance into the rectum through a pair of tiny openings.

The glands are emptied naturally when the rectal sphincter muscles contract during a bowel movement. Pet owners are usually unaware of this occurrence, since the odor of the anal glands is masked by the odor of the cat’s stool; however, cats can tell the difference.

Cats sniff rear ends as a greeting and obtain vital information from the anal secretions. Is this cat a friend or foe? Is she going to be a good “date”? Is he aggressive? Is she feeling ill? And because the odor is unique to every cat and serves as a form of identification, two cats can quickly determine if they have met before.

The very act of sniffing rear ends can establish the foundation of a feline relationship. A more assertive cat will usually initiate the sniffing, while the less assertive cat waits her turn. A submissive cat may end the sniffing first and retreat. Some cats like to limit the information they give out and will simply sit down and clamp their tails over their rectums, reducing the odor they emit.