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How Dogs Perceive The World Through Smell


By Nancy Brannon, Ph.D.

Since traditional foxhunting is all about finding the quarry (fox or coyote) through the foxhounds’ keen sense of smell, Alexandra Horowitz’ latest book Being A Dog might interest foxhunters and give more insight into how foxhounds operate. Her research may also interest field trial enthusiasts, whose sport is also dependent on the ability of bird dogs to find the quarry (quail). Horowitz told us by email: “I don't focus particularly on bird dogs or foxhounds. (I love the “cold-trailer” label!) I do follow a Lagotto hunting truffles. But all the detection-dog work holds for hunting dogs as well.” 

Horowitz was interviewed on NPR’s Fresh Air on October 4, 2016 about her book. Here are some highlights from the interview.

In Being a Dog Horowitz explains her research on the mechanics of canine smell and how dogs use their noses to understand the world around them. Dogs are particularly drawn to “smell-rich environments,” such as fire hydrants and tree trunks.

Horowitz says that all dogs have the ability to create “a picture of the world through smell,” primarily because of the way their noses are designed. A canine’s nose is “stereoscopic,” she explains, which means that each nostril is controlled separately, allowing the dog not only to detect a particular smell, but also to locate it in space.

The dynamics of how a dog breathes are different from the way humans breathe. Dogs inhale through the nostrils, but exhale through the side slits of their nose. That process allows odors that they’ve inhaled to stay in the back of the nose a little longer. Humans can exhale a smell with a single push of air. But dogs don’t push all the smell out with a single exhale. “It’s like a circular breathing of smelling. It also creates a little puff on the ground, a puff of air that might allow more odor molecules to come up toward their nose to be sniffed,” Horowitz explained.

The musculature of the dog’s nose also allows the dog to get a different odor sample with each nostril, especially up close, which might be why they bring their noses close to things. Many dogs have a long snout, which humidifies and filters the air and rushes the air to the back of the nose. Humans have a similar, but less complex, apparatus.

At the end of the nose, between the eyes, both dogs and humans have a patch of tissue called the olfactory epithelium, which has receptor cells that “grab” the odors and send signals to the brain. The difference is that the dog has hundreds of millions more receptor cells than humans do, which may explain their increased acuity.

The types of detection work that dogs do are really stunning. Dogs can be trained to find explosives, drugs, missing people, and even particular types of diseases, e.g., melanoma. There’s a budding research program in training dogs to detect various cancers on the breath, in urine, blood, and on the skin.

Smells tell time, too; strong odor is likely a newer odor. A weaker odor is something that was left in the past. So being able to detect the concentration of a smell, dogs determine not only what it is, but also how long ago it was left. Thus, foxhunters have a term for hounds who are particularly good at detecting older odors – cold trailing.

Read the full interview at:

About the author: Alexandra Horowitz is an Adjunct Associate Professor in the Department of Psychology at Barnard College in New York City, since 2004. Her research is in dog cognition. She is currently testing the olfactory acuity of the domestic dog, through experiments in natural settings, and examining dog-human dyadic play behavior. Horowitz has a TED Ed lesson on “How dogs see with their noses” at: She has had articles published in The New York Times, The New Yorker, and Smithsonian magazine. Read her academic profile at:  Visit the Dog Cognition Lab at:

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