Dogs can train us to have a better sense of smell

Our daily tug of leash war goes like this. I tell Chico we’re taking a left. He yanks right, wet black nostrils burrowing in loamy leaf piles. Me versus a 15-pound Havanese, incensed by scent.

Today, I let him win.

That’s because I have fresh appreciation for his sniffing behavior, after reading a new book, “Being a Dog: Following the Dog into a World of Smell,” by Alexandra Horowitz, a professor of cognitive science who runs the Dog Cognition Lab at Barnard College. In it, she explains the elegant engineering of the dog’s olfactory system and how familiar canine behaviors — licking, sneezing, tail-wagging — have associations with smell. Horowitz also describes how she trained herself to enhance her inferior human sniffing ability.

On a recent afternoon at Riverside Park in Manhattan, I met Horowitz and Finn, her affable, glossy black 9-year-old mixed breed. There she — and he — shared some sniffing insights that have since made my walks with Chico more intriguing and fun.

Dogs sniff, humans sniff, what’s the difference?

“There are many ways to sniff, and the human method is not the best,” Horowitz said. Sniff researchers (yes, you read that correctly) have found we have about 6 million olfactory receptors; dogs have 300 million. Humans sniff once per second-and-a-half; dogs, five to 10 times a second.

“They even exhale better than we do,” Horowitz continued, describing a sort of doggy yoga breath. Dogs exhale through the side slits of their nostrils, so they keep a continuous flow of inhaled air in their snout for smelling. “This gives them a continuous olfactory view of the world.”

And while our schnozzes get the job done, the dog’s snout is superb. Dog sniffs are designed to send odor-carrying air along its length, she said, humidifying, warming and cleaning it along the way to the back of the nose.

Why do dogs love to lick stinky toes?

Licking is related to smell, Horowitz said. Dogs and many other animals have a second smell system called the vomeronasal organ (VNO) above the roof of their mouth and below the septum dividing the sides of the nose.

Sniffs pick up airborne odors, but the sensitive VNO can detect the smell of molecules that have been absorbed in tissue. One way is through licking. “They like to get a full measure of the smell, all of its details,” Horowitz said, explaining why dogs get so up close and personal with one another and us. “They have a great instinct for analyzing it.”

Why do dogs love to roll around in things that smell repulsive?

One theory is that their sense of smell is really a complex motor system related to the brain. And so, Horowitz said, when Finn alights upon a rotting squirrel corpse in the park, the smell that fires up the olfactory lobe in his brain also travels to the motor cortex and tells him to lean his whole body into the found object of desire.

“There’s no ‘noxious scent’ receptor in the dog’s brain,” she added. “But they do seem particularly interested in rolling in smells that we find somewhere between off-putting and disgusting.”

Is wagging related to smell, too?

Yes. Many of a dog’s identifying smells are in the anal glands. Those sacs transmit how a dog is feeling — anxious? playful? — and the essence of who the dog is. To greet one another, said Horowitz, as Finn demonstrated obligingly, hailing a goldendoodle named Polly, “dogs wag, basically dispensing their personal odors from their rumps.”

Horowitz writes about how she took Finn to remedial “nosework” classes. She soon saw that he found huge delight in locating objects by scent.

To show off this skill, she had hidden a vial with an anise-soaked cotton swab in a tree trunk along our walking route. As we approached it, she scratched Finn’s ears, unclipped his leash and gave him a command: “Find it!” He bounded off, sniffing furiously. At last, standing on his hind legs, he discovered it.

“He lights up,” she said. “He’s a middle-aged dog but he had no problem turning back on his sense of smell.”

How can pet dogs exercise their sense of smell?

“Take a smell walk with them.” Horowitz said. “Let them lead the way and smell and linger. Let them sniff each other. There’s a pleasure for owners in letting a dog be a dog, to acknowledge their dogness. They put up with a lot of our humanness.”

How can humans exercise our own sense of smell?

In the book, Horowitz writes about her experiments in recharging her olfactory system. Her advice for us is comparatively simple.

“Take a cue from the dog,” she said. “Put your nose in things and take dedicated sniffs. Name the smells. Every expert smeller I met practiced it thousands of times. Pick up a bottle of perfume. Crush leaves between your fingers.

“I enjoy smells more now. They’re no longer good or bad. They tell me about the world. That’s as close as I get to being doglike.”

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