Why Do Dogs Have Such a Strong Sense of Smell?
Ever wonder why your dog can easily sniff out something that you can’t smell at all? Rebecca Frankel, author of War Dogs, explains the fascinating reasons for your canine’s superior snout.
If you know what to listen for, the sound is unmistakable. The attuned human ear can hear when a dog has found the sought-after odor usually long before he gives his final alert. And depending on the training and the kind of detection work, the dog will either sit at the source of odor or lie down to the ground. For obvious reasons, search-and-rescue dogs will bark. A practiced handler will recognize his dog’s personal tells—the dog may twitch his ears or his movements may slow down and become more deliberate, or he may even have an “I’m definitely on odor” expression—but it’s really the sound that is the big giveaway. It’s the deep, staccato inhale and then the rush of a perfunctory and heavy exhale. It is the sound of satisfaction. It is the sound of discovery.
The Science Behind the Nose
The canine nose is a masterful creation; all earthly schnozes are not created equal, anatomically speaking. While the average dog has roughly 220 million scent receptors in his nasal cavity, the average human has around 5 million. The canine sense of smell is a thousand times more sensitive than a human’s. One of the best visual analogies of the dog’s acute sense of smell is given by author Mark Derr in Dog’s Best Friend: “Unfolded and flattened, the smell receptors from the average dog’s nose could cover it like a second coat with hair dragging on the ground.”
Even the way a canine nose functions is more developed than ours. A dog’s nose has four passages, two inner ones and two on the outside, almost like gills. The inner canals pull in the scent and then exhale to the outer, so that the exhaling air doesn’t disturb the ground or source of the next odor, allowing always for the intake of fresh scent. Humans, in contrast, have just the two nasal passages, and what goes up comes back out again the same way. (We can of course draw breath through our mouths when we ingest or exhale oxygen, but it is not the best way to smell, although it is one of the best ways to use our sense of taste for certain foods—by orthonasal, or mouth, breathing. On the other hand, while dogs are great perpetrators of mouth breathing, they’re not using it for scent. Though they have good reason to do so. Dogs actually pant through their mouths to cool off, whereas we humans sweat.) That always-damp and cool-to-the-touch quality of the canine nose also has its purpose; moisture that is “secreted by mucous glands in the nasal cavity captures and dissolves molecules in the air and brings them into contact with specialized olfactory epithelium inside the nose.”
Making a Memory
It’s not that we humans don’t use our sense of smell, but as a sense it’s powerful for very different reasons. Scent recalls memories and awakens our emotional subconscious. We associate different odors, good and bad, with people and places—and there’s no accounting for taste in what we relish either. My father, for example, loves the smell of a good barn populated with fragrant livestock. As a family driving the New England interstates, we inevitably passed open pasture, and as we did, my father would lower his window to get his fill of the open air heavy with manure, while my sister and I groaned and pinched our noses. He was taking in the scent of his childhood on the farm and all the memories that came with it—we children of the suburbs were just smelling, well, shit.
Most people don’t make a conscious effort to imprint particular or special smells, to file them away for later use—they register more like background noise, though invariably certain things punch through the ether, people and places we are reminded of by the power of scent. But perhaps we should take our lead from dogs and program our brains to catalogue smells in more proactive and useful ways. In one of the great old Disney movies, The Parent Trap (with Hayley Mills and Maureen O’Hara), when one of the girls—Susan, pretending to be her twin sister, Sharon—meets her grandfather for the first time, she sniffs the lapel of his jacket with such earnest investigation that he pulls back. “My dear, what are you doing?” he asks. To which she replies, “Making a memory.” She puts her nose back to his tweedy chest, calling out the scents she identifies. “When I’m quite grown-up,” she tells him, “I will always remember my grandfather and how he smelled of tobacco and peppermint.”
Making a memory of a smell, or imprinting odor, is exactly how a dog learns to seek out bombs, weapons caches, narcotics, missing persons, and, sadly, human remains. The process involves training a dog to associate odors with a reward. Dogs become visibly excited when they’ve discovered an odor they have been trained to detect. The less disciplined ones will cast their heads back, looking, waiting, and watching for the Kong (or tennis ball, or treat) they know is coming, too eager to contain themselves.