© 2024 WOSU Public Media
Play Live Radio
Next Up:
0:00 0:00
Available On Air Stations

From Fire Hydrants To Rescue Work, Dogs Perceive The World Through Smell


This is FRESH AIR. I'm Dave Davies in for Terry Gross. It's probably happened to you a hundred times. You arrive to visit someone's home, and a friendly dog walks up and gives you a good sniff. Dogs are trained to detect traces of explosives and illegal drugs as well as pests like bedbugs and even certain cancers because of their acute sense of smell. Today we're going to hear about what makes it possible for dogs to perceive scents that we can't. Alexandra Horowitz is best known for her best-seller "Inside Of A Dog."

She's also the founder of the Dog Cognition Lab at Barnard College. Terry spoke to her last year about her latest book now in paperback about dogs' sense of smell. It's called "Being A Dog."



Alexandra Horowitz, welcome to FRESH AIR. Dogs have been used to hunt and track people. But now because of their great sense of smell, they're being used in new ways, being relied on in ways that they've never been relied on before. Give us some examples.

ALEXANDRA HOROWITZ: The types of work that dogs now do as detection dogs is really stunning. And I don't think we've reached the capacity of what dogs are able to do. So dogs are, as we know, able to find explosives and drugs with some high acuity. They also are really good at finding us, finding missing people, whether dead or alive. But they're also used to detect goods that are brought into the country illegally, whether that's mango or bananas. They're also used to find animals whose population we're trying to count through detecting their scat.

They can smell out illicit cellphones or computers, if trained on the electronic components. So they're really used widely as detection dogs.

GROSS: They're being used now to determine if certain tumors are cancerous?

HOROWITZ: Yeah, one of the most amazing things is that, accidentally, researchers discovered that dogs could detect melanoma. The accident was that there were individual dogs who were persistently smelling something on their owners. When their owners finally went to a doctor and had it checked out, it turned out to be a melanoma. And so since that time, there's been a budding research program in training dogs to detect various cancers on the breath, in urine, in blood and on the skin. And most of these programs report very high levels of success. Dogs are definitely able to detect whatever it is in the cell that makes it cancerous.

GROSS: And, of course, dogs are being used to detect explosives in train stations and airports.

HOROWITZ: You almost can't go to an airport anymore without seeing a dog. So it's becoming a familiar part of our life. And I think that's just the tip of the iceberg.

GROSS: And bedbugs, dogs are being used to detect bedbugs.

HOROWITZ: Yeah. I'm sorry to say...

GROSS: Thank you, dogs.


HOROWITZ: We even had a bedbug detection dog come through our house and find nothing, happily. But there are some dogs, especially beagles, who are trained to detect not just the bedbugs but the trace of the bedbugs. In other words, the skin slough - the casing sloughed off or the excreta of the bedbugs and determine if you have a problem before you are bitten.

GROSS: You write that explosive detection dogs can smell a trillionth of a gram of an explosive. I mean, that's such a minuscule amount. Can dogs smell, like, the remnant of an odor in such a microscopic size?

HOROWITZ: It does seem as though what they're detecting at that really low, low, low threshold is kind of almost the trace left behind by an object. You know, if we thought of putting a cup down that you've held on a table and picking it up, we would think that the cup is gone. But at some low level, the cup has left a trace of itself. And if you touch a surface and lift your hand, you have left a trace of yourself that has an odor. And the dogs can detect that.

GROSS: So compare a dog's nose with our nose. Let's start with the fact that dogs' noses have stereoscopic capability. They can smell separately with each nostril.

HOROWITZ: Precisely so, I mean, starting at the nostril, their nostrils are doing a little bit better work than ours are. They have all this musculature - we do as well with our nose, but theirs really allows them to get a different odor sample with each nostril, especially up close, which might be why they bring their noses close to things, one of the reasons. Then they have this amazing long snout, many dogs, which humidifies and filters the air and kind of rushes the air up to the back of the nose.

We both have that same apparatus, but ours is less complex. And at the end of the nose, right sort of between the eyes, we both have a little patch of tissue called the olfactory epithelium, which has the receptor cells, the ones that really grab the odors and are going to send the signal to the brain. The dog's, it has just hundreds of millions more receptor cells than ours does. And that's probably partially responsible for their increased acuity.

GROSS: So let's get back to the stereoscopic nostrils. Why do they have separate control of each nostril? How does that help them?

HOROWITZ: It makes sense to have the nostrils work independently just the same way as it makes sense to have our eyes get a different snapshot of the world so that we can create three-dimensional representation of what's out there. Binocular vision is the same as kind of stereo olfaction for a visual creature. That allows them to not only detect whether a smell is there but where in space it might be. Is it more to my left? Is it more to my right? Is it in front of me? Is it behind me? - creating a picture of the world through smell.

GROSS: The dogs' exhale is different from ours, too, and adds to their ability to detect and identify smell. Can you describe the exhale, what happens there?

HOROWITZ: I love the fact that not only is the dog sniff different than ours but their exhale is different. I mean, it goes so deep, the differences between us. And in this case, researchers looking at the fluid dynamics of airflow found that dogs exhale through the side slits of their nose. So they inhale through the nostrils but exhale through the side. And what that does is it allows the odors that they've inhaled to stay in there a little bit longer in the back of the nose.

When you want to get a smell out of your nose, you can exhale it out. You can kind of push it out with an exhale. But dogs don't push all the smell out with a single exhale. It's like a circular breathing of smelling. And it also creates a little puff on the ground, a puff of air that might actually allow more odor molecules to come up toward their nose to be sniffed.

GROSS: And they also have what you describe as a second nose under their nose.

HOROWITZ: Right. They have a vomeronasal organ, which is a small sac above the roof of the mouth under the nose, which allows them to detect other chemicals, especially things like pheromones and other hormones which are water soluble, which aren't volatile, aren't - don't evaporate in the air. And so that allows them, like other animals that have the vomeronasal organ, to detect hormones on other members of their species and even other species.

GROSS: So now that you've told us a little bit about how dogs perceive the world through their sense of smell, let's talk about some of the things they can smell that we just can't. I mean, you've talked about detection dogs. But, like, you say normal dogs, dogs who aren't working dogs, can smell, for instance, that it's afternoon or they can smell that it's a new day. They can kind of tell time through their sense of smell. How do they do that?

HOROWITZ: I think this is one of the more intriguing things about imagining the olfactory world to a creature like a dog. Smells tell time. In other words, a strong odor is probably a newer odor, laid down more recently. A weaker odor is something that was left in the past. So in being able to detect the concentration of a smell, they're really seeing not only what it is but how long ago it was left. So when being able to detect the concentration of a smell, they're really seeing not only what it is, but how long ago it was left. So the past, for instance, when you walk outside your door is underfoot, who's walked by, what, you know, skin have they sloughed, leaving some evidence of their voyage, what animals have passed by? And the future, in a way, is smelled on a breeze from up ahead or around a corner.

So I feel like time is rubber-banded for dogs through smell. And it also allows them to detect things which we don't think are really visible yet, like dogs often are said to be able to detect an upcoming storm. One of the reasons this might be is that when a low-pressure system moves in, the air above the ground kind of feels extra roomy and the earth loosens its grip on odors within it, and they become volatile. They evaporate and go up in the air. And the dog can detect that. And you might see a change in their behavior when they notice this new smell.

GROSS: But how can they smell that it's afternoon? What does afternoon smell like compared to morning?

HOROWITZ: Well, smells in a room change as the day goes on. Hot air rises, and it usually rises in currents along the walls and will rise to the ceiling and go kind of to the center of the room and drop. And so if we were able to visualize the movement of air through the day, what we're really visualizing is the movement of odor through the day. In the mid-afternoon, you might feel tangibly on your skin that - or see through the light in the window that it's afternoon, and the sun is halfway in the middle of the sky. The dog, I think, can smell that through the movement of that air through a room.

GROSS: If you're just joining us, my guest is Alexandra Horowitz. She's the author of the best-seller "Inside Of A Dog." Now she has a new book called "Being A Dog" that's all about dogs' sense of smell. She also founded the Dog Cognition Lab at Barnard College. We'll be right back after a break. This is FRESH AIR.


GROSS: This is FRESH AIR, and if you're just joining us, my guest is Alexandra Horowitz. She's the author of the best-seller "Inside Of A Dog," and now she has a new book called "Being A Dog" that's about how a dog understands the world through its sense of smell. She's also the founder of the Dog Cognition Lab at Barnard College.

If dogs are so good at detecting odors, why are they not repelled by their own smelliness when they get really filthy or they rolled in something really foul?

HOROWITZ: (Laughter) It's not obvious that it is foul or smelly in that sense to a dog. In other words, I think when you try to imagine a world made of smells, smells become less binary than they are to us. For us, they're often really pleasant or really unpleasant. You know, I like freshly baked bread, and I really don't like garbage that's sat on the summer in - on the street in New York City. But, for dogs, those smells are just information. They're information about what's out there, and I don't think they levy the same judgment on smells.

Just like when you walk into a room and you see a lot of visual information, we're not saying, oh, that's really a bad color. That's really a bad image. That's really a great one. We're just seeing it as a room.

GROSS: You know, when I put lotion on my hands when my cat is on my lap or sitting next to me, I wonder will the cat still know it's me because I've just put something on my hands that's going to mask my odor and replace it with the lotion odor? And I'm wondering, like, with dogs, when you've, like, come out of the shower after having soap - you know, used a fragrant soap or if you've put lotion on your hands or say you're somebody who wears perfume or something, does the dog recognize that you're still you?

HOROWITZ: I think that's a great question. We are, I think, somewhat hidden by these smells that we layer on our smell. But our smell, the smell of us, is profound to the dog. I mean, each one of us, no matter how clean you are, really stinks. We're giving off a haze of odor and molecules that the dog not only detects, but comes to recognize as us. So a perfume or a fragrant soap might put them off for a second. There might be a moment of lack of recognition, but if they can get a little closer or get on the other side of the - of a breeze, then they'll recognize you instantly. We all have a really - an identifying smell to the dog.

GROSS: We've all had the experience of going to visit the home of a friend where we haven't been before. The friend has a dog. The first thing they do when you arrive is greet you by smelling your crotch, which is embarrassing for everybody. So why do dogs do that?

HOROWITZ: It's a really smelly place. I mean, dogs are extremely good at honing in on the parts of us that happen to smell. And we secrete a lot of smells from a couple of parts of our body - the crotch, the armpits, the mouth.

You know, one of the things you can do when you don't like that, which most people don't, is give them something else to smell. You know, they might be preoccupied with the smell of your ear, for instance. We have lots of glands that give off odors around our face, and that might suffice to be information about you. That's all the dog is trying to get, information. I love that we often feel like the dog is being impolite in that case. And many people will not unreasonably train their dogs not to do that. But I also see it as just the dog's way of discovering who you are, and we are our smell to them.

GROSS: So you did this amazing experiment with what you call a pee poll in a New York park (laughter). What was the poll? And what were you looking for?

HOROWITZ: Right. We set up a pee post, essentially, which is just a place where a dog might mark, might leave an identifying bit of pee. And we set a camera up to capture instances of dogs visiting this. And what I'm trying to do is do some basic research about what dogs are doing when they mark.

What we know from some research of feral dogs and free-ranging dogs is that dogs aren't doing what we mostly think they are doing when they mark, which is marking territory. Dogs don't have territorial-marking pee like wolves do. They'll go around their home range and pee right around the perimeter so that any intruder will know that they're entering someone else's territory. What would be that home range for dogs? It's obvious that they no longer have that kind of perception of the world. They don't have home ranges. They do mark along shared paths, what researchers like to call runways. So if you encounter a lamp post or a fire hydrant or a tree trunk on your regular walk and lots of other dogs, too, chances are that dogs will mark all of these places.

But what they're doing with this information, we're not exactly sure. So I was looking at all the behaviors around dogs' sniffing of these marked spots of the pee post and what they do afterwards.

GROSS: What did you learn?

HOROWITZ: Well, thus far, it looks like there are a couple of interesting characteristics of the marking. First, they sniff a lot more than they mark. So it's not that every dog comes, notices that someone's been there before and then has to leave their own mark. It's really not territorial or dominance related. Also, they often look up after they sniff. And it's really hard to see, I think, for most owners when their dog is looking somewhere what might actually be happening, which is often that they're smelling somewhere. And if you look, their noses are working. You can see their noses working. They're probably smelling after the dog who has left that mark.

My favorite observation is just that dogs don't come back to check again later. You know, they don't go to smell their own pee and see, has anybody covered this? - which I find fascinating.

GROSS: So have you basically found that dogs identify themselves with pee in the same way that, like, a graffiti-writer might to say that they were there (laughter)?

HOROWITZ: I would say that I don't know conclusively what they're doing yet. They might be leaving a little message, like a message you tack on a bulletin board, for other dogs with information about who they are and what they've eaten today and how healthy they are and what sex they are and maybe even how old they are and so forth. But they never come back to check on other messages that are left in response. So it's not obvious to me why they would leave those messages. It might just be a vestige of having been wolves or something like wolves thousands of years ago.

GROSS: You know, we talked earlier about how working dogs are being used in incredible ways now - to sniff out bed bugs, to detect certain cancerous tumors. In your book, you mentioned that some working dogs are being used to sniff out in advance when somebody is about to have an epileptic seizure or whether they're about to go into diabetic shock, which is - it's pretty remarkable things that these dogs can do. But at the same time, you point out that some domestic dogs are losing some of their sense of smell. Why are they losing it?

HOROWITZ: People really don't encourage dogs to smell very much. One - the one thing that detection dogs do is go and find an odor that they've been trained on. In all circumstances - every day for a detection dog's life is them getting up, being brought to a situation, told to find an odor of some sort, finding it perhaps and getting to play with a toy as a reward. So they're expressly told to smell.

But in a pet dog's life, they're usually told not to smell, right? They - as you say, when they greet someone - a visitor to the house - you know, they go to smell the person and they're discouraged from smelling the person. If - many people don't like to be licked by their dogs. If they're sniffing things by a tree trunk or a fire hydrant outside, their dogs - their owners might pull their dogs away. Now it's becoming even more popular to not have dogs sniff each other up close for fear that one dog might be too aggressive or maybe just impolite.

So they're discouraged from smelling in their ordinary life often. And I don't think they lose their ability to smell, but they lose their predisposition to smell. They're kind of living in our visual world, and they start attending to our pointing and our gestures and our facial expressions more and less to smells.

DAVIES: Alexandra Horowitz is the founder of the Dog Cognition Lab at Barnard College. Her book "Being A Dog" is now out in paperback. We'll hear more about dogs' sense of smell after a break. Also, David Bianculli reviews "Alias Grace," the new Netflix series based on a Margaret Atwood novel. And David Edelstein reviews "Lady Bird," the new semi-autobiographical film directed and written by Greta Gerwig. I'm Dave Davies. This is FRESH AIR.


DAVIES: This is FRESH AIR. I'm Dave Davies in for Terry Gross. We're listening to Terry's interview recorded last year with Alexandra Horowitz. Her book, "Being A Dog," about how dogs rely on their sense of smell to perceive the world around them, is now out in paperback. She's also the author of the best-seller "Inside Of A Dog" and founder of the Dog Cognition Lab at Barnard College, where she conducts research on dog behavior and perception.


GROSS: After you started doing research about how a dog uses its sense of smell, how it perceives the world through its sense of smell, you started taking your dogs on smell walks. What do you do and why are you doing it?

HOROWITZ: Well, I really am trying to counter what I and lots of owners have done our whole lives, which is discourage smelling. And in fact, instead, I'm trying to embrace it. So on a smell walk, really, I just let the dog choose what we're going to do and where we're going to go and how long we're going to stay there.

So sometimes we don't get off our front step for a little while because as soon as you open the door, the dog is faced with a new day. And the air holds odor that - where a trace of who or what's passed by. Then we might spend a little time with a little tree guard - the iron railing that surrounds a tree - which has leavings from, presumably, other dogs who have passed by.

And I just let the dog take charge. Sometimes our walks are pretty much standing around actually, but I think that the dog is enjoying himself.

GROSS: You know, dogs recognize us from our odors, but we don't really want to smell. You know, if you say to somebody, you smell, that's usually not a good thing. Have you changed your attitude about your own body odors?

HOROWITZ: I've changed my attitude about all odors, really, from all this practice intentionally smelling. I mean, I never was one to wear a lot of perfume to begin with. Now actually, I like perfumes more as a kind of odor one might wear, but not because it would cover up my own odor. I think I am a little less worried, maybe to the chagrin of those around me, about having an odor. I just see it as a natural part of being a biological creature.

And I really do celebrate, as I saw sometimes with these olfactory experts, some of the bad smells in the way that I didn't used to celebrate them. So a smell of garbage, for instance, is more just information about the fact that there's garbage near rather than being something hugely off-putting and offensive - that's the way I used to find it - and something that affected me. And now I'd feel, oh, well, yeah. I mean, there's garbage, and that's the strong smell of garbage. And isn't that interesting?

GROSS: So I'm interested in the Dog Cognition Lab at Barnard that you created and still run. What kinds of experiments do you do there?

HOROWITZ: I started this lab because I used to do simple experiments on my own, but students really wanted to be involved. And there was this burgeoning world of dog cognition, which 20 years ago, didn't exist, but had a little momentum. And so I basically asked people to join me in the lab so that I could do slightly more complex experiments. I do really simple behavioral experiments, which try to ask and answer questions that I'm interested in. And I also do a lot of natural observations of dogs, for instance, interacting with their owners in play or playing themselves to see if I can deconstruct what's going on in those interactions.

Some of the experiments I do are testing, for instance, anthropomorphisms, attributions that we make of dogs. One of my favorites was of the guilty look. Dogs show this guilty look, pulling their ears back and pulling their tail under their body or turning away. Often, owners know when they've done something wrong. So it's fair for people to say that dogs look guilty. But I thought, that's a strange attribution. How can we be sure that dogs are guilty? And so I did a little test to see if the guilty look popped up only when they'd done something wrong or in any other circumstance.

GROSS: What did you find?

HOROWITZ: And it's a really simple experiment. And I found that the guilty look showed up more often when they were being scolded or about to be scolded by their owners, whether or not they'd done something wrong. And so it looks like we really prompt the dogs to put on this look, which is probably more aptly described as a submissive look or a concerned look, than a guilty look. I'm not saying that dogs don't feel guilt. They very well might, but this look isn't showing us that.

GROSS: Tell us about the dogs you have now.

HOROWITZ: Upton is a large, mixed-breed mongrel dog - probably a Plott Hound and Great Dane mix - well, well mixed - that we got. We got him when he was 3-and-a-half years old. And he's a really goofy, large, sweet dog. And I also have Finnegan, who we've lived with for about eight years, who's also a mixed-breed, maybe Lab mix. I consider Finnegan kind of a professional dog. He's much more cooperative in listening to us, wants to kind of follow our lead a lot more. And he's the one I took with me in this book to do a few smelling projects because I was really interested in how much we could kind of open up his nose and make him a smelling dog again.

GROSS: How did you find your dogs?

HOROWITZ: Both of my dogs we found in shelters. I went to shelters - I don't go to shelters very much because it's really hard for me to not adopt an animal when I see an animal at a shelter. They all look so wonderful. But we went to a shelter in Queens and found Finnegan long ago as a puppy. He was sick. And we brought him out, and he leaned against me, and boy, that really grabbed me. So we took him. And then a few years later, I had my son. And Finnegan was displaced as the primary child in the family. And so a few years after that, we decided to get another dog - probably as a companion, we thought, for Finnegan. And we went again to a shelter and met this great, galumphing, funny creature, who became Upton. And now we have a two-dog family.

GROSS: With Upton, how did you know that he was the dog for you?

HOROWITZ: It was not obvious, I would say, with a 3-and-a-half-year-old dog who'd been given up twice to a shelter. But he recognized me after just a few minutes. We met him. We played with him in a little room. We put him back. And then I returned, and he recognized us. And we know this about dogs, that they actually form attachments really fast in shelters if they see somebody again and again. And this large dog, showing recognition and wagging happily, you know, thunk (ph), thunk, thunk on the bottom of his cage is - you know, my heart can't handle that.

GROSS: (Laughter).

HOROWITZ: We had to take him home.

GROSS: Did you have any reservations about adopting a dog that was 3-and-a-half years old and had already been returned once to the shelter?

HOROWITZ: No. But, you know, it's great to get a slightly older dog. Puppies are just wonderful. But there are so many dogs that are returned to shelters that I know that if I was going to get a second dog, I wanted to contribute to reducing those numbers. And dogs are so flexible. You know, this dog, Upton, has some fears. He's not a perfect city dog. You know, the sounds of a city are difficult for him. But he's so agreeable, ultimately, as most dogs are, and sort of cooperative in working their way into the family, that a lot of things can happen to a dog, and they'll still turn and trust the next person and give it a shot.

GROSS: So you wanted to find a dog who'd been returned to a shelter. Did you go into the shelter and say, who's been returned to you?

HOROWITZ: Well, all these dogs...

GROSS: Show me a dog nobody seems to want.


HOROWITZ: Well, a big dog is an especially hard sell, I think. And older dogs even older than that are hard sells because people want to have a lifetime with the dog, which is understandable. But, yeah, we did go looking for especially an older dog. And, you know, I like the look of him. You have to like the way a dog looks and the way they act around you and the feeling that they're somehow recognizing you is important, and he had all of those things.

GROSS: Has your approach to training dogs changed over the years?

HOROWITZ: I should say that my dogs are not really trained, per se. I don't - I'm not - I never - I'm not a dog trainer, and I've never been that concerned with making them super polite. You know, they - I train them to do the things that they need to do in emergency and to protect themselves and others. They can come, and they'll sit for me and so forth. But, you know, I'm less concerned about keeping them off the bed or the couch than maybe I would have been when I first was a dog owner.

In fact, I don't try to keep them off the bed or the couch. It's perfectly fine with me if they're sitting when we're sitting. And I understand the urge. That's where I like to sit, too. And I - I'm very willing to have them off leash and run around as long as they'll come back to me and not interfere with other people. So I don't think that they're really heavily trained. I like them to be dog-like.

GROSS: So some readers know your dog Pumpernickel from your previous book, and Pumpernickel is no longer with us. How did Pumpernickel die?

HOROWITZ: She died of being very old, which I was fortunate. You know, that almost never happens. She died at almost...

GROSS: How did you know it was time?

HOROWITZ: Well, she had slowed down to the point of stopping, essentially, and she was 17 years old. It wasn't surprising when she stopped enjoying things that she usually enjoyed like, you know, a little lick of peanut butter on a finger or a small game of rough and tumble or jostling each other. And I knew that she wasn't really experiencing life.

GROSS: And did you take her to the vet or did the vet come to you?

HOROWITZ: A vet came to us. It's really one of the more heartbreaking things I've had to do in my life. And, you know, her life ended with me. And when she died, I thought - I was impossibly sad. I mean, I really wrote "Inside Of A Dog" kind of as a tribute to her, thinking about her. And I probably spent a year, which is maybe not extraordinary for people who live with dogs, really, really glum and sad and thinking that it was impossible that she was gone. And that's about how long it took before I decided to get another dog as well, that I did realize that I couldn't live in a space that didn't have another, you know, happy, breathing, wagging creature in it. And that's how we went and met Finnegan.

GROSS: I want to thank you so much for talking with us.

HOROWITZ: It's been my utter pleasure. Thank you, Terry.

DAVIES: Alexandra Horowitz is founder of the Dog Cognition Lab at Barnard College. Her book about dogs' sense of smell, "Being A Dog," is now out in paperback. Coming up, David Bianculli reviews "Alias Grace," the new Netflix series based on a Margaret Atwood novel. This is FRESH AIR.

(SOUNDBITE OF PAQUITO D'RIVERA'S "CONTRADANZA") Transcript provided by NPR, Copyright NPR.