Dogs may be man’s best friend, they may be cute and entertaining but admit it, they are also gross. They smear your favourite dress with drool – usually right around the crotch, they shed enough hair to fill a duvet and they spend half their time with their noses flitting from one butt to another. And as if sticking their noses into each others behinds isn’t enough, they do it with such glee and enthusiasm. But why? Is it pure curiosity? Do they just like the smell? A bit of surprisingly complex science can help us get to the bottom of this fishy behaviour.

Starting with the dog’s most impressive instrument – their nose. We all know that dogs have a heightened sense of smell. They are certainly a lot more impressive than us humans. Take this visual analogy: Say you could see perfectly up to 1/3 of a mile, a dog would be able to see just as clearly for 3,000 miles. This is largely down to tiny receptors in a dog’s nose. They have up to 300 million olfactory receptors, while humans have only up to six million. These olfactory receptors are the places where molecules attach and begin sending messages to the brain. This is the same process for humans (think how much you salivate when you smell bacon even if you can’t see it).

In addition to the huge number of smell receptors in their noses dogs have a specialised organ, which we don’t have, called Jacobson’s organ. Jacobson’s organ is located at the base of the nasal cavity and can detect pheromones – particularly those associated with mating.

Interestingly odours received in the Jacobson’s organ are handled via a different route to those taken in through the olfactory receptors.

So dogs are equipped with some fairly spiffing sniffing tools but why is smelling so important? Many people’s pooches are clever and good at communicating what they want. But hard as they may try dogs can’t talk so, as with most non-human animals, they rely on other types of communication. Dogs use the old butt-sniff as a means of introduction and conversation. From one swift inhalation they can tell the diet, gender, emotional state, health, immune status and even genetics of their compatriot. Though the evolution of spoken language is a game changer for human ability to communicate, we still use our noses too. Kissing, for example, has evolved to enable chemical communication between humans akin to the butt-sniff.

This begs the question... why the butt? To complement their high tech sniffer, dogs have a pouch of chemical messages just waiting to be sniffed called the anal sac. Within the anal sac the apocrine gland contains short chain acids that are extremely fragrant. These wafty molecules are like the index for what is going on inside the dog.

Gross as it may be I can’t help but admire the complex and sophisticated equipment a dog uses to understand, and communicate with, other dogs.

We may be in front in terms of language but for overall communication dogs are coming up the rear.

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