Every meeting of dogs usually starts with an introduction that involves a good butt sniff. What data are they gathering with this form of greeting?
Indeed, when they leave their scent on something and smell scents left by other dogs, what information are they getting?
Big-brained we humans might be, but we’re little-nosed. We’re visual creatures, interpreting the world first through sight; dogs are olfactory creatures, seeing that same world as a smell landscape.
The difference highlights how hard it can be for us to imagine that dogs are sniffing anything at all on the pavement when we see ‘nothing there’, or how baffled we are when they go to sniff another dog’s rump for the seventh time.
To begin to understand it, look at where your gaze lingers when you meet another person: do you look once and then quickly look away, never to let your gaze alight on them again?
When you visit a museum, do you stand in front of a painting for a mere moment before turning away, or do you sometimes linger for minutes or hours, examining the image from different directions, at different distances, even exclaiming with pleasure or wonder?
As we see the world, so dogs smell it. They have hundreds of millions more olfactory receptors in their noses than we do, each of which grabs odorant molecules out of the air and converts that smell into neural signals to the brain.
Their noses are long warming and humidifying chambers lined with special tissue that allows them to deconstruct multifaceted smells, even before they reach the receptors.
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Dogs can sniff up to seven times a second, and have a brilliant way of exhaling: out the side slits of their nostrils, so their exhale does not interfere with their steady inhale of the smelly vista in front of them.
Simply put, the anatomy and physiology of dog sniffing should begin to allow us to see how they’re operating on a different olfactory level than we are.
When dogs sniff each other, they’re finding out about each other. (And by the way, males tend to approach an unknown dog’s rump first, while females most often aim for the head first.)
Their vision is perfectly good (they’re nearsighted, have two-colour vision and especially keen night vision), but it’s in our signature smells that reveal who we are to an olfactory animal. Everyone has a smell and, at minimum, our chemical exudation includes information about our sex, our health and what we’ve recently eaten.
It has information about our stress levels and our emotions; for female dogs, it has information about their estrous cycle. In essence, it has information about who we are.
That’s what a dog is sniffing out in another dog – and when they're greeting you (you may have noticed that they love to stick their snouts in some of our smelliest areas first: our mouths and our groins).
Some ask why, if the dog’s sense of smell is so keen, don’t they stand at a polite distance and sniff surreptitiously at each other.
It makes more sense to wonder why we humans find it off-putting to smell each other, when most mammals are happy to get close for a sniff. The closer you get, the more information you can perceive: the brush strokes of the scene, not just the overall colour or form.
Since nearly everything has a smell, and as most animals (including the human animal) slough off skin and fur as we move, the ground holds a tale of our passing, for any animal willing to sniff closely.
Indeed, research has shown that tracking dogs can determine which way a person has fled by sniffing just five footprints, as they’re able to distinguish the amount of odorant left behind in the first (older) and fifth (newer) print.
In this way, dogs can smell the passage of time: older scents are on the ground and more degraded; newer scents are brighter and, maybe, still in the air.
Not just a tracking dog but also your dog can detect, on leaving your flat, if someone has recently passed by, from sniffing the air. But they can also smell them in odour fallen on the ground, or, if the passerby is a dog, in the urine they’ve usefully left on a tree trunk.
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