Inside of a Dog_ What Dogs See, Smell, and Know - Alexandra Horowitz [31]
What, then, do these noses enable the dog to smell? What does the world look like from the vantage of a nose? Let's start with the easy stuff for them: what they smell of us and of each other. Then we might be ready to challenge them to smell time, the history of a river stone, and the approach of a thunderstorm.
The smelly ape
Humans stink. The human armpit is one of the most profound sources of odor produced by any animal; our breath is a confusing melody of smells; our genitals reek. The organ that covers our body—our skin—is itself covered in sweat and sebaceous glands, which are regularly churning out fluid and oils holding our particular brand of scent. When we touch objects, we leave a bit of ourselves on it: a slough of skin, with its clutch of bacteria steadily munching and excreting away. This is our smell, our signature odor. If the object is porous—a soft slipper, say—and we spend a lot of time touching it—putting a foot in it, clutching it, carrying it under an arm—it becomes an extension of ourselves for a creature of the nose. For my dog, my slipper is a part of me. The slipper may not look to us like an object that would be terribly interesting to a dog, but anyone who has returned home to find a ravaged slipper, or who has been tracked by the scent they've left thereon, knows otherwise.
We needn't even touch objects for them to smell of us: as we move, we leave behind a trail of skin cells. The air is perfumed with our constant dehumidifying sweat. Added to this, we wear in odor what we've eaten today, whom we've kissed, what we've brushed against. Whatever cologne we put on merely adds to the cacophony. On top of this, our urine, traveling down from the kidneys, catches odorous notes from other organs and glands: the adrenal glands, the renal tubes, and potentially the sex organs. The trace of this concoction on our bodies and our clothes provides more uniquely specific information about us. As a result, dogs find it incredibly easy to distinguish us by scent alone. Trained dogs can tell identical twins apart by scent. And our aroma remains even when we've left, hence the "magical" powers of tracking dogs. These skilled sniffers see us in the cloud of molecules we leave behind.
To dogs, we are our scent. In some ways, olfactory recognition of people is quite similar to our own visual recognition of people: there are multiple components of the image responsible for how we look. A different haircut or a newly bespectacled face can, at least momentarily, mislead us as to the identity of the person standing before us. I can be surprised what even a close friend looks like from a different vantage or from a distance. So too must the olfactory image we embody be different in different contexts. The mere arrival of my (human) friend at the dog park is enough to set me smiling; it takes another beat before my dog notices her own friend. And odors are subject to decay and dispersal that light is not: a smell from a nearby object may not reach you if a breeze carries it in the other direction, and the strength of an odor diminishes over time. Unless my friend tries ducking behind a tree, it's hard for her to conceal her visual image from me: a wind won't conceal her. But it might conceal her from a dog momentarily.
When we return home at a day's end, dogs typically greet our cocktail of stink promptly and lovingly. Should we come home after having bathed in unfamiliar perfume or wearing someone else's clothes, we might expect a moment of puzzlement—it is no longer "us"—but our natural effusion will soon give us away. Dogs are not alone among