Butt Sniffing 101

“Hello! Do I know you? Have we met before?”
“Hey there! Do I know you?? Lemme smell to find out…”

Butt Sniffing.  It’s gross to most humans, but it’s very important to our canine comrades.

Derriere sniffing is just one of the many fascinating forms of chemical communication in the animal kingdom.  Animals all around the world use chemical communication to communicate.  Pheromones are the source of this communication!

Pheromones are chemicals released by living organisms that send information to other organisms of the same species via scent.  They’re used to scent mark, attract mates, claim territory, find prey, and identify other animals.  Pheromones can be released as alarms, food trails, sex lures, and much more.  Plants, vertebrates, and insects communicate in this chemosensory way.

Our dogs and cats (and even hedgehogs!) are just as sensitive to these pheromones, and they decipher them using a very cool method!  Like many reptiles and other mammals, these animals have a “scent collector “in the roof of their mouth that’s called a Jacobson’s Organ, or a vomeronasal organ. (Which, by the way, is absolutely one of the coolest tools in the animal kingdom.)  This organ is used by many species to send chemical scents directly to the brain.

Snakes use their Jacobson's Organ to detect pheromones in their environment, similarly to how dogs do!
Snakes, like many animals, use their Jacobson’s Organ to detect pheromones in their environment! Snakes are actually tasting the air when they stick out their tongues.

The Jacobson’s organ is useful in the process of communicating chemical messages between members of the same species. The organ helps snakes hunt and track their prey. Much evidence suggests that this organ may also be involved in the detection of chemical signals related to aggression and territoriality in some species.

Fun Fact:  Elephants touch the tips of their trunks to the Jacobson’s Organ (inside the roof of their mouth) to engage their chemosensory perception of things in their environment.  Lions use it for sensing sex hormones.

A great view of an elephant's Jacobson's Organ.  I have had the pleasure of an Asian elephant named Gene, letting me feel hers. They are so cool!
A great view of an elephant’s Jacobson’s Organ.  Elephants touch the tip of their trunk to this organ to discern scents in their environment.  I have had the pleasure being able to feel one of these organs, thanks to a very special Asian elephant named Gene.

This same organ recognizes chemicals as they enter a dog’s nose, via circular sniffs through each nostril. This organ then interprets the pheromones collected. It’s sensitive enough to not confuse fecal matter scent with pheromones.

Underside view of a dog's Jacobson's Organ
Underside view of a dog’s Jacobson’s Organ

According to the American Chemical Society, when dogs get their derriere sniffing on, it’s really all about one dog literally sniffing out important information about the other.  Find out why “Bacon is to people, as butt sniffing is to dogs” in the video below:

Fido Fact: Dogs possess up to 300 million olfactory receptors in their noses, compared to about six million in us.  Proportionally speaking it’s 40 times greater than ours.

Feline Fact: A cat’s sense of smell is 40x stronger than ours.  Scent is crucial when it comes to social situations, locating prey & maintaining safety.  Scent is also crucial when it comes to evaluation of food.

Scent-Secreting Sacs!

Our pooches have pouches called anal sacs.  These sacs are a pair of small, kidney-shaped structures on each side of the anus.  These sacs hold glands that secrete chemicals.  Every dog has a unique scent “signature” created by the secretions of its anal sacs.  This unique scent not only distinguishes one dog from another, but it also reveals the dog’s sex. Genetics and the state of their immune system can influence the aroma of these sacs.

All predators, whether they are canines or felines in the wild or skunks in your backyard, have anal glands. They just use them differently. . In dogs and cats, every time a stool is passed, it should put enough pressure on the anal glands that some of the secretion is deposited on the surface of the stool. Other dogs and cats are then able to tell who has been in the neighborhood, just by sniffing the stools they find. Additionally, dogs and cats recognize each other by smelling each other in the general area of the anus, since each animal's anal glands produce a unique scent.


When an animal passes a stool, it should put enough pressure on the anal glands so that some of the secretion is deposited on the surface of the stool. Other dogs are able to tell who has been in the ‘hood, just by sniffing the stools they find.  Dogs can smell these anal sac scents when they are nose-to-rear as well.

cat anal sac_anal glands_how cats smell_cat urine_cat spraying_cat communnication

Cats also have two little anal glands on each side of the rectum that release a very strong-smelling liquid to mark the cat’s stool as it passes through. And cats have scent glands on their paws pads, cheeks, and head! You can read more about these here.

cat flehming response_jacobson organ
A feline experiencing a flehmen response

The flehmen response (/ˈfleɪmən/; German: [ˈfleːmən]), also called the flehmen position, flehmen reaction, flehming, or flehmening. This is a behavior in which an animal curls back its upper lip exposing its front teeth, inhales with the nostrils usually closed and then often holds this position for several seconds.  It may be performed over a site or substance of particular interest to the animal (e.g. urine or feces) or may be performed with the neck stretched and the head held high in the air.

The Flehmen response is performed by a wide range of mammals including ungulates and felids.  The behavior facilitates the transfer of pheromones and other scents into the vomeronasal organ (VNO, or Jacobson’s organ) located above the roof of the mouth via a duct which exits just behind the front teeth of the animal. The word originates from the German verb flehmen, to bare the upper teeth. The flehmen response often gives the appearance that the animal is grimacing, smirking or laughing.

horse _Flehmen response
A horse in Ireland displaying a Flehmen response when I am offering him food


Intraspecific communication
The main reason for, or function of flehmen is intraspecific, or within-species communication. By transferring air containing pheromones and other scents to the vomeronasal organ (VNO), an olfactory-chemosensory organ located between the roof of the mouth and the palate, animals can gather chemical “messages”.

The response is perhaps most easily observed in domestic cats and horses; both exhibit a strong flehmen response to odors.  Stallions usually smell the urine of mares in estrus whereas the male giraffe’s flehmen response includes actually tasting the female’s urine. Elephants perform a flehmen response but also transfer chemosensory stimuli to the vomeronasal opening in the roof of their mouths using the prehensile structure, sometimes called a “finger”, at the tips of their trunks.


Interspecific communication
The flehmen response is not limited to intraspecific communication.  Goats have been tested for their flehmen response to urine from 20 different species, including several non-mammalian species.  This study suggests there is a common element in the urine of all animals, an interspecific pheromone, which elicits flehmen behavior. Specifically, chemical pheromone levels of a modified form of androgen, a sex hormone, were associated with the response in goats.

Other animals which exhibit the flehmen response include buffalo, tigers, tapirs, lions, giraffes, llamas, hedgehogs, rhinoceros, giant pandas, and hippopotami.


When it comes to companion animals such as dogs and cats, they recognize each other by smelling one another in the general area of the anus, since each animal’s anal glands produce a unique scent.  Sniffing another derriere is just another form of chemical communication. Think of this behavior as “speaking with chemicals”.  It’s how they learn about another dog or cat’s diet, gender, and even their emotional state!

So the next time you see your dog or cat getting a good whiff of another’s derriere or  doody, let him/her get their sniff on!  It’s not gross; its purely instinctual and it’s a very effective form of communication!  Your cat or dog will thank you for letting him/her Bbe themselves.


Sniffing Butt
“oooh, what do you have going on?! Let me get a good whiff and find out!”






Recommended Video:

How dogs “see” with their noses!

2 thoughts on “Butt Sniffing 101

  1. Pingback: Was It Out of Spite? Think Again. | Conscious Companion

  2. Pingback: Anal Glands, Superman, and Polyester Fleece | Conscious Companion

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