Exercising and Enhancing the Senses - Smell

We begin with the sense of smell, which plays the lead role in a dog’s experiential world. A dog’s world is a continuous cacophony and symphony of odors swirling around and into their noses. As “nosed animals,” a term we borrow from Alexandra Horowitz, dogs live in, and are consumed by, a world of smells.1 Our human sensory experience is dominated by sight, so to understand the world from our dog’s perspective, we really need to use our imagination and think about “seeing” the world through our nose. When we walk dogs on a leash and they stop to smell something, it is almost like they are stopping to read a very interesting news headline or hear some important neighborhood gossip. Dogs gather information first and foremost through their nose, not primarily through their eyes or ears.

And it seems like dogs are always gathering olfactory information, not just when they have their noses obviously pinned to the ground tracking a scent, but even when they’re just standing around looking like they aren’t doing much of anything. The nose never stops. On a walk through the neighborhood, a dog is collecting all kinds of important information from sniffing: They learn about the other dogs who have previously been there, and how recently; they might learn about female receptivity and even perhaps what the other dogs were feeling. Dogs might also be sniffing while they are asleep; their noses never go to bed.2

The dog’s nose is an amazing adaptation. In fact, the canine nose is a virtual work of art, like many other organs that evolve via natural selection. The noses of many breeds of dogs are much bigger than human noses, and the dog’s olfactory center in the brain is proportionately larger than that of humans; this means that more of the dog’s brain is dedicated to processing olfactory information. Dogs have 125 to 300 million olfactory receptors compared to our measly 6 million. On average, their sense of smell is about a thousand times more sensitive than ours.3 They can track many smells at the same time, and they sniff approximately five times a second. Alexandra Horowitz has suggested that if we were to spread out a dog’s nasal epithelium (the lining of a dog’s nose), it would cover their entire body, while ours would only cover a mole on our shoulder.4

A dog’s nose sends incoming air into two separate paths, one for breathing and one for smelling. (Humans have no choice but to smell and breathe through the same pathway.) Unless dogs are panting, they breathe in through the nose, not through the mouth.

Each dog is different, and their sensory experiences and needs may vary. A dog’s breed or breed characteristics don’t necessarily determine what will make the dog optimally happy, but it’s worth thinking about the shape of your dog’s nose and what gets them sniffing and snorting. Hound dogs such as English pointers and bassets are highly motivated by smells, and the opportunity to explore the world with their nose may be an even higher priority for them than for individuals of brachycephalic breeds, like pugs and bulldogs, who have short skulls with compressed noses. Like humans, short-nosed dogs tend to spend more time breathing through their mouths, so they likely take in and process less olfactory information than their longer-nosed compatriots. Dogs with very foreshortened snouts can also suffer from obstructed breathing caused by congenital defects, such as collapsed nostrils, which makes smelling more difficult. Because short-nosed dogs can’t make full use of their olfactory sense, we need to try extra hard to enhance their world of smells and to offset their deprivation in this sensory realm with extra attention to other senses, such as taste and touch.5

Lots of people wonder whether dogs sense the passage of time. Do they know the difference, for example, when their human companions have been gone from the house for five minutes or five hours? Scientists don’t have a clear answer to this question, but one interesting clue comes from the nose. Horowitz suggests that dogs are sensitive to changes in the strength of odors that are evaporating. Smells degrade over time and odors will grow fainter. So, for a dog, how faint a smell has become may indicate how much time has elapsed since the odor was in full bloom.6 Dogs understand the scent landscape in very complex ways and can distinguish between newer and older scent trails. They can track scents that are up to a week old. How refined or well-developed this method of sensing time is awaits further study.

LET DOGS SNIFF !

Off-leash dogs spend about a third of their time sniffing.7 On-leash dogs aren’t typically allowed to sniff for nearly this long. How often have you seen someone angrily tugging on the leash, trying to make their dog “keep up” on a walk? This is a form of sensory deprivation. In a Whole Dog Journal story about leash-walking behavior, the author’s casual observation was that around 85 percent of the time dogs were pulling or dragging their humans down the street or vice versa.8 Sometimes a dog wants to surge forward and get somewhere more quickly than the owner; sometimes a dog stops to intently investigate some smell and their impatient companion is the one tugging the lead, saying, “Come on! Let’s go! I’m in a hurry.” Or, “What are you doing? There’s nothing there!” This second remark indicates a lack of knowledge about what dogs are sensing — we may not see anything of interest, but our dog certainly smells something fascinating. These complaints also embody a typical mismatch between our expectations and desires on a walk and those of our dog. Dogs aren’t in a hurry to pee and poop and go back inside. After all, for many dogs, the daily walk (if they are lucky enough to get one) is their only time to really be out in the world and engage with it.

One easy way to enhance your dog’s freedom is to accommodate their need to smell. When they are outside, whether on a walk or not, allow them ample time to exercise their nose and sniff to their nostrils’ and brain’s content. This is one of the simplest enhancements we can provide. Let them sniff ! If there are places where your dog can be off leash, by all means give them this opportunity to walk or run at will, following their own olfactory agenda. When walking with a dog on leash, as much as possible let your dog set the pace. If your dog wants to linger over a bush, a clump of grass, or a fire hydrant, let them. Remember, some of the things that we might consider unsavory, like poop or pee, are very interesting to our dogs. Let dogs smell whatever they want, even if it seems disgusting; pee and poop are especially important because they contain a great deal of canine-relevant information.

Indeed, regardless of the apparent reason, when a dog resists our prodding and insists on sniffing, they’re clearly telling us they’ve found something highly salient to them. In the context of animal behavior, the “salience” of a stimulus is the extent to which it stands out among other stimuli; the more salient, the more prominent or important the stimulus.

THE IMPORTANCE OF PEE-MAIL

For dogs, peeing is like leaving Post-it Notes around the neighborhood for other dogs to read, and sniffing pee spots is like reading the notes left behind by other dogs. Dogs like to smell the urine of other dogs, and they like to pee on all sorts of things, including on top of the urine of other dogs. This is called overmarking, and dogs may do it to cover up the scent of other dogs or to highlight their own scent. Urine is an extremely important tool that allows dogs to talk with one another about who was there and when, who’s in heat, and perhaps how they are feeling. It’s also possible that dogs recognize one another via urine, but research confirming this is not yet available. This is another reason not to expect your dog to pee once and be done. When dogs pee a little bit here, there, and everywhere, they aren’t being indecisive; they might be leaving messages.

It was long believed that dogs marked their own territory when they peed, so that peeing on something meant: “This is mine; this is my turf. Be aware and stay out.” However, we’ve learned that peeing has a much broader set of meanings for dogs. Some urinating may be territorial, but much of it is not. Sometimes dogs pee because they want to mask the odor of another dog’s urine or be sure their scent is the one that others detect. And of course, sometimes dogs pee simply because they need to go.

We also know that dogs find the urine of other dogs more interesting than their own urine, and they will spend more time investigating a urine spot made by another dog than urine they left themselves.9 Dogs often get so into sniffing urine it’s impossible to get their attention; even a tasty treat won’t work. Marc’s dog Jethro earned the nickname Hoover because of his tendency to vacuum up the whiff of potent pee.

Dogs and their wild relatives will occasionally lift a leg without depositing any noticeable urine. This is called “dry marking.” It isn’t clear exactly why dogs dry mark, but Marc has hypothesized that leg lifting might be a visual signal that tells other dogs that pee was deposited, even when it wasn’t. In this way, pee can be saved for when it is most needed. It’s not uncommon to see dry marking followed by leg lifting and peeing within a few seconds, so in fact, the dog is not out of urine. Marc and his students showed that dogs dry mark more often when there are other dogs around who can see them, indicating this might be a visual display.10

Dogs also often scratch the ground after peeing or pooping. Dogs have scent glands in their paws, and when they scratch, they might be trying to send an olfactory message to other dogs by spreading the scent from their paws or by sharing the odor of the pee or poop they deposited. Scratching also leaves a visual mark on the ground. Ground scratching could be yet another form of social communication, and taken together, peeing, pooping, and ground scratching are a good example of how dogs may use composite signals to enhance their messages to other dogs, by using both olfactory and visual components. In other words, let your dog finish their message — give them time to scratch after they have peed or pooped — before continuing your walk.

LET ’EM ROLL

As offensive as it may be to us, the prospect of rolling on a pile of freshly mowed grass, a half-dried fish carcass, cow or elk feces, or some other nasty thing is very appealing to a dog. This is part of their natural behavioral repertoire and something their wild relatives also do.

Why do dogs roll in stinky stuff ? We really don’t know. They may be masking their own odor, or they may be making a statement about themselves by parading around with a strong or different odor. Whatever the reason, this is a behavior that dogs are motivated to perform, so we should let them do it, at least occasionally. Of course, this is one behavior that might need to be constrained at times, since most of us will want our smelly friends to have a good warm bath before reentering the house, and we may not have time (and excessive bathing is hard on dogs’ skin). Since your dog likely won’t associate rolling in stink with the inevitable bath that follows at home, don’t expect the bath to serve as a lesson for the future.

PROTECT THEIR SCENT IDENTITY: AVOID DOG PERFUMES AND DEODORANTS

An advertisement for Petco reads, “Keep your pup smelling delicious between baths with Petco’s selection of dog perfumes, colognes, and deodorant sprays.” But Jessica’s dog Bella would be the first to tell you that she really doesn’t like to smell like cherry or tea tree. She would much rather smell like Bella. A dog’s scent is their identity. We may not be aware of our own odor, but dogs are most certainly tuned in to their own scent profile (and to ours). So, in the spirit of allowing dogs to be dogs, let your dog smell like a dog.

Groomers often use heavily scented shampoos and conditioners to make a dog smell “nice,” which means that they carry or exude an odor that we like. Nobody really knows whether these strong artificial smells are aversive to dogs, but it’s likely, given the sensitivity of dogs’ noses. Odors are powerful triggers for people, and we aren’t remotely as smell-oriented as dogs.

Because dogs communicate with one another through odor, changing their smell by washing it off or covering it up with perfumes will likely make communication with other dogs more challenging.

One very important thing to consider in trying to create a comfortable home environment for our dogs is to think broadly about odors. We might find comfort in scented sheets, whereas dogs likely prefer bedding that smells familiar and doggy. When we leave dogs alone for the day, they might be comforted to be surrounded by odors that relax them, which means their own doggy odors and those of their favorite humans or of other pets in the home.

This is something to remember when or if you move to a new home, take a dog on vacation, leave your dog at home with a friendly dog-sitter, or take your dog to their favorite canine B&B (when they can’t join you on a trip): Bring along a favorite dirty pillow or stinky stuffed toy — something with odors that will be familiar — to help your dog feel more at ease and less anxious.

AVOID OLFACTORY OVERLOAD

Because of their olfactory sensitivity, it’s reasonable to ask if dogs can overdose on too many odors coming in at the same time or one after another. We know that dogs find all sorts of smells stimulating, but can they overindulge and suffer from too much of a good thing?

While it may be hard to imagine, dogs can suffer from sensory overstimulation that compromises their well-being. Being exposed to a strong odor for an extended period or being continuously bombarded with the same odor may lead to a feeling of sensory overload. Dogs, when their noses are full of a strong smell, may also be unable to recognize other odors that may be important to them. These may be odors signaling danger or telling them that a none-too-friendly dog is around. When there’s too much background noise, we can’t hear other people talk and we can’t hear ourselves think. Strong smells may be like irritating background noise to our dogs.

As of now, there has been no research into whether dogs find strong odors aversive or whether odors can compromise their well-being. But it is worth thinking about. Powerful body perfumes, strong disinfectants, heavily scented candles, or spray air fresheners might essentially be nasal assaults on our dogs (and often, when overdone, on humans as well). Does this mean that you should never wear perfume or cologne if you live with a dog? Never burn incense? Never douse the dog bed with Febreze? No, it doesn’t, but your dog will likely appreciate it if you show restraint, and it might be a good idea to skip the Febreze. Dogs are already awash in artificial scents, from the laundry detergent we use to the formaldehyde in our carpets and furniture to the mint in our toothpaste. Dogs trying to live in a human-dominated world have their senses assaulted every second of the day, and we can help by giving them a break from too many strong, artificial scents.

People who work with dogs are already thinking about these things. For example, aware that the strong smells of chlorine and other disinfectants are aversive to many dogs, veterinary clinics (following the “fear free” model developed by Dr. Marty Becker) are using cleaners, such as hydrogen peroxide, that don’t have a strong chemical odor. These cleaners are also designed to reduce the fear pheromones left behind by other dogs who have visited the clinic.11 Some veterinarians, trainers, shelters, and researchers are also experimenting with aromas that dogs find calming, such as lavender.12

BUTTS: A CRITICAL CANINE COMMUNICATION CENTER

One behavior in which many dogs love to engage is butt sniffing. It may be mysterious to us — the siren call of the anal area — but this is undoubtedly a strong motivator for our dogs. To us, all dog butts may look (and smell) pretty much the same, but to our dogs, certain hind ends create a special buzz and require closer inspection.

Why is butt sniffing important for dogs? We really don’t know much from formal studies, but it’s likely that dogs gain information about individual identity — Joey smells like this, Lela smells like that. It’s also possible they gather information about gender or about the reproductive state of the dog they’re sniffing. While a dog’s nose is traveling around the butt region, they’re also picking up information from the anal glands that might tell them something about the other dog’s emotional state, such as whether they’re afraid or stressed out. All in all, though we find it rather uncomfortable and awkward, the entire anal area is a critical canine communication center, and we need to honor this doggy fact.

Human groins also are a part of the dog’s olfactory landscape. We all know that dogs have a tendency to stick their noses into human groins, much to our own embarrassment. Groining dogs are not perverts; they’re detectives. A human’s groin is a cocktail of interesting and information-rich odors. From a dog’s perspective, sticking a nose into someone’s groin is not rude; rather, it’s a normal part of saying hello, gathering information, and exchanging pleasantries. While we can teach our dog not to do this to strangers, we also shouldn’t get our knickers into a knot if and when they do.

BURPS, GAS, AND DOGGY BREATH

We often laugh when a dog burps, but other than the sound effect, burps are not usually all that offensive. On some occasions, burps might serve a social function. Marc’s friend Marije terEllen tells him that Benson, a five-year-old Bernese mountain dog, likes to come up to her, face-to-face, look her in the eyes, and burp. He seems to get a kick out of doing it, and he doesn’t burp at other times. Is this his way of saying “hello” or “I love you”? Or is he just poking fun at his human? Marije insists that Benson is not mimicking her or her daughter, Arianne.

Like burps, farts are normal. Some people think dogs like to fart, but this isn’t really known and there’s no reason to think so, or not any more than we do. Some find dog farts gross, and some use dogs as scapegoats for their own indiscretions, but the bottom line is that all dogs fart. Sometimes a dog will seem surprised when passing gas or will “admit” to a fart, such as by turning around and looking curiously at their own butt or perhaps by leaving the room. Usually, dogs simply proceed as if nothing happened. And that’s what we should do, too. A dog shouldn’t be punished for farting, such as by scolding and banishing the dog to the backyard. This won’t be understood by the dog and will seem arbitrary.

That said, excessive flatulence or burping can also be a sign of a serious medical problem and isn’t a laughing matter. Know what’s normal for your dog and what isn’t. Farting is often a sign of gastrointestinal upset: It may indicate that a change in diet or a certain food isn’t agreeing with the dog’s stomach; it might indicate a GI illness, such as inflammatory bowel disease, or food allergies. As dogs age, they often become more flatulent because they begin to lose muscle tone and control in their sphincter (something that also happens to people as they age). Jessica’s fifteen-year-old dog Maya is pretty much constantly farting, and Jessica can always tell what room Maya is in just by smell.

Dog breath is another source of amusing complaints for us, and as if in on the joke, dogs seem to love to get up close and personal and breathe right into our faces. Generally, adult dogs have worse breath than puppies; the somewhat distinct and sweet smell of “puppy breath” is related to a lack of bacteria in the mouth. When adult teeth start coming in, the lovely scent of puppy breath disappears and is replaced by plain old dog breath. Some level of bad breath is normal for a dog, but particularly smelly breath is another warning sign that something might be wrong. Tooth decay, gingivitis, infected teeth, and other serious medical conditions can lead to bad breath. If you notice a change in your dog’s breath, and if it smells especially foul, your dog should be checked out by a veterinarian.

One of the biggest favors you can do for your dog is to take care of his or her teeth by creating a habit (at least weekly) of tooth brushing. Few dogs enjoy having their teeth brushed, but if you start when a dog is a puppy and make the experience fun, it helps establish a routine. Flavored toothpastes and lots of treats and praise can help make the brushing experience a positive one. Your dog can enjoy a healthy set of teeth and gums, and you will be rewarded with reasonably tolerable dog breath.

by Marc Bekoff and Jessica Pierce.

Note

1. Alexandra Horowitz, Being a Dog (New York: Scribner, 2016), is all about dogs’ noses.

2. For more on a dog’s nose, see Frank Rosell, Secrets of the Snout: The Dog’s Incredible Nose (Chicago: University of Chicago Press, 2018), and Horowitz, Being a Dog.

3. Although dogs have superior sniffing skills compared to humans, the long-standing assumption that humans have poor olfaction turns out to be more myth than fact. The nineteenth-century anatomist Paul Broca noted that humans have a small olfactory bulb, relative to overall brain size compared to other mammals, and interpreted this to mean that we relied very little on our olfactory sense — that we are “nonsmellers” and that we suffer from what later came to be called microsmaty, or “tiny smell” (a defect that Freud thought made humans susceptible to mental illness). Broca’s dismissal of the human sense of smell led to an overall scientific neglect of this human sensory skill. New research in neuroscience suggests that the human olfactory system may be just as complex and discriminating as that of other mammals. See John P. McGann, “Poor Human Olfaction Is a 19th-Century Myth,” Science 356 (May 12, 2017): 597, http://science.sciencemag.org/content/356/6338/eaam7263.

4. Horowitz, Being a Dog, 48.

5. Having a compromised sense of smell is only one of the potential issues faced by brachycephalic or short-snouted dogs. Because the upper jaw of the skull has been compressed (through selective breeding), the soft tissue of the nasal passage is crammed within the skull, and this can lead to difficulty breathing. These dogs are at high risk of developing brachycephalic obstructive airway syndrome, which can be life threatening for the dog and expensive for the owner. Several studies have shown that many owners of brachycephalic dogs do not believe their dogs have breathing problems, despite clear physical symptoms. Instead, they think that the snorting and snuffling sounds made as the dog breathes are just “normal” for “this kind of dog.”

Veterinary groups are concerned about the increasing popularity of some brachycephalic breeds. For example, Kennel Club registrations of French bulldogs shot up from 692 in 2007 to 21,470 in 2016. The British Veterinary Association has launched a campaign to educate prospective and current owners of these short-nosed breeds about how to identify common health problems. Prospective owners are encouraged to consider a different breed altogether or a crossbreed, or to look for healthier versions of the brachycephalic breeds, which have been bred to have slightly longer snouts.

See, for example, Nicola Davis, “Think Twice about Buying ‘Squashed-Faced Breeds,’ Vets Urge Dog-Lovers,” Guardian, January 5, 2018, https://www.theguardian.com/lifeandstyle/2018/jan/05/think-twice-about-buying-squashed-faced-breeds-vets-urge-dog-lovers; and Royal Veterinary College, “Worrying Numbers of ‘Short-Nosed’ Dog Owners Do Not Believe Their Pets to Have Breathing Problems,” Phys-Org, May 10, 2012, https://phys.org/news/2012-05-short-nosed-dog-owners-pets-problems.html.

6. Horowitz, Being a Dog.

7. Sophia Yin, in Secret Science of the Dog Park, directed by Jeremy Nelson (Canada: Stornoway Productions, 2015); see Bekoff, “Dog Park Confidential,” chap. 8 in Canine Confidential.

8. Nancy Kerns, “Walking the Dog On Leash: Why Is It So Hard for People?” Whole Dog Journal, October 22, 2017, https://www.whole-dog-journal.com/blog/walking-the-dog-on-leash-dragging-pulling-21725-1.html.

9. Because dogs failed the so-called “mirror test” developed by Gordon Gallup in the 1970s to test self-recognition in chimpanzees, it was long assumed that dogs didn’t have a sense of “self” as separate from “other.” But in “ecologically relevant” self-recognition tests based on olfaction, dogs clearly distinguish between “me” and “you.” See Introduction, note 15.

10. Marc Bekoff, “Butts and Noses: Secrets and Lessons from Dog Parks,” Animal Emotions (blog), Psychology Today, May 16, 2015, https://www.psychologytoday.com/us/blog/animal-emotions/201505/butts-and-noses-secrets-and-lessons-dog-parks; and Marc Bekoff, “Scent-Marking by Free Ranging Domestic Dogs: Olfactory and Visual Components,” Biology of Behavior 4 (1979): 123–39; also see Bekoff, “Who’s Walking Whom,” chap. 5 in Canine Confidential.

11. See Fear Free (https://fearfreepets.com); and Janice K. F. Lloyd, “Minimising Stress for Patients in the Veterinary Hospital: Why It Is Important and What Can Be Done about It,” Veterinary Sciences 4, no. 2 (June 2017), https://www.ncbi.nlm.nih.gov/pmc/articles/pmc5606596.

12. Marc Bekoff, “Dogs’ Noses in the News: Scents Reduce Stress in Shelters,” Animal Emotions (blog), Psychology Today, April 21, 2018, https://www.psychologytoday.com/us/blog/animal-emotions/201804/dogs-noses-in-the-news-scents-reduce-stress-in-shelters.