"Why Do Dogs Sniff Each Other?"
Is Butt-Sniffing the Equivalent of a Canine Handshake?
Originally published in slightly different form on July 13, 2009 at PsychologyToday.com.
A Dog's "Handshake."
It’s said that dogs sniff each other as a kind of canine equivalent to the human handshake; an otherwise meaningless “greeting ceremony”  which reportedly started in medieval times as a way of checking the other guy for weapons. Our canine companions are said to do this for similar reasons; it signifies that both animals are willing to start out on friendly terms.
But is it really just a social gesture? Does it have an adaptive purpose? Will knowing the true reason for this behavior tell us anything useful about the dog’s way of seeing the world? And perhaps more importantly, will it tell us anything about ourselves?
We know that at least 33% of a dog’s brain is devoted to processing olfactory information while in humans that figure is closer to about 5%.
Marc Bekoff wrote here recently in “Yellow Snow Can Tells Us About What a Dog’s Nose Knows.” that “[a dog’s nose] can distinguish T-shirts worn by identical twins, follow odor trails, and are 10,000 times more sensitive than humans to certain odors.”
“Odors are powerful stimulants,” Bekoff continues. “Although my late companion dog, Jethro (aka Hoover), enjoyed visiting his veterinarian, he showed fear if he went into an examination room where the previous canine client was afraid.”
Steven R. Lindsay writes, “Olfactory information is highly durable in dogs. They exhibit evidence of recognizing the scent of the mother and the breeder after years of separation, social memories that may persist throughout a dog’s life.” (Handbook of Applied Dog Behavior and Training: Adaptation and Learning, 2000, p. 228.)
So if a dog’s nose can pick up information from yellow snow, from the fear that hangs in the air after another dog leaves a veterinary examination room, from scents left behind by the shoes of an escaped prisoner, or from lifting its nostrils to the wind, why would a dog need to stick his nose directly into another dog’s snout, genitals, and nether regions to garner social information? Couldn’t he do that at a “safer” distance? And if the emotional memories sparked by familiar scents are so durable, why would dogs need to continue sniffing each other every time they meet even after they’ve already established a social relationship?
From the Top Down and the Outside In
Dog trainer and natural philosopher Kevin Behan has a unique way of looking at canine behavior. Most of us tend to view such phenomena from the top down or from the outside in. As a result we overcomplicate things. Behan does just the opposite. He sees things from the inside out, and in so doing he’s developed a very simple theory of “behavior as energy,” sort of the E = MC2 of animal consciousness if you will, except it would probably be written as C = ME2, where C is consciousness, M is momentum, and E is emotional energy. (I just made that up, of course; I don’t think Behan has such an equation.)
In the “Why Dogs Do What They Do“ section of his website, Behan makes a very interesting and apt observation, “When people meet and greet, they shake hands or touch in some way, and they exchange pleasantries. And when dogs meet and greet, they smell each other. However people don’t reintroduce themselves periodically throughout their interaction or every time they meet especially if they know each other well, whereas dogs smell each other each and every time they meet, no matter how well they may ‘know’ each other.”
Like a lot of Kevin’s observations this one comes as both a bit of a surprise and a “Huh, I hadn’t thought about it but that’s true...” realization.
I had three dogs staying with me this weekend. Two of them, Dougie and Muskoka, see each other at least twice a week. They spend a lot of time together, they’ve known each other for years, they’re best buds, they don’t need to “shake hands” every time they run into one another. Yet on Saturday, when Dougie’s owners dropped him off, the first thing he and Muskoka did, right there on my front stoop, was sniff each other.
Why do dogs need to do this?
A Simple Observation
Behan says it’s a way of grounding themselves. “Anytime there is ... any change, any stimulus or stimulation, and especially when stressed, dogs need to smell something.”
That’s a simple and yet very intriguing observation. And you can see it for yourself in the way a dog who’s momentarily frightened when a book falls to the floor, for example, will first react to the noise and then cautiously, and somewhat mysteriously, go over to sniff the offending object. I’ve also seen a dog notice that another dog is whimpering in his sleep. And she’ll come over, and, while the other dog is still dreaming, very gingerly sniff his snout.
Behan explains, “[Any] change in the dog’s sensory perception of a situation generates nervous activity in its brain, and this of course is neuro-chemical electrical energy. My proposal is that this electrochemical energy acts just like electricity in that it wants ‘to run to ground.’”
He also says that too much electricity creates a disconnect between the “big brain” in the head and the “little brain” in the solar plexus, and that inhaling the smell of something is a way of restoring internal balance. 
“Smelling is that primal,” says Behan. “It allows the dog to connect with its ‘self’ and quite literally feel the ground beneath its feet.”
It’s Primal In Humans Too
What happens when you stop and smell the roses? It makes you feel good; you can feel your chest expand. What happens when a tantalizing smell comes wafting toward you from a pizza joint? You feel it in your gut. What happens when you find the scent of your lover’s perfume on a scarf she’s left behind? You experience a rush of sexual desire. Whenever we smell something pleasant we’re instantly taken “outside of ourselves;” we leave behind all the thoughts that were buzzing around in our brains, and we experience, if just for a fleeting moment, what it’s like just to be in a body.
As has been discussed in several previous articles here,  human beings have an innate tendency to anthropomorphize animals, i.e., “when dogs sniff each other it’s the canine equivalent of shaking hands.” But I think that in order to truly understand canine behavior we sometimes need to dogthropomorphize ourselves.
Spanish philosopher Jose Ortega y Gasset once pondered the handshake. “Man—let us never forget, was once a wild beast, and, potentially he continues to be one to a greater or lesser degree. Hence the approach of man to man was always a possible tragedy. What today seems to us such a simple and easy thing—one man approaching another—was until recently a dangerous and difficult operation. So it was necessary to invent a technique of approach.” (Jose Ortega y Gasset, Man and People, 1963, p. 207)
I had an important meeting the other day, and I was a bit nervous coming into the room. Then, as I shook hands with everyone there, I tried to tune-in to what effects, if any, it had on me. And sure enough, each handshake actually made me feel less nervous and more balanced, as if the soles of my feet were planted more firmly on solid ground. (I’m not sure that happens every time we shake hands, but it was an interesting feeling, and one I had never noticed before.)
Dogs can’t “categorize” things. For instance, while we might say that Dougie and Muskoka are “friends,” and they’re certainly friendly toward one another, they don’t put things into conceptual chunks, store them in a mental library, and retrieve them for future reference. In other words, they don’t think of themselves as friends, they just feel it. We, on the other hand, can sometimes think too much. That’s why it’s so pleasant to escape our thoughts when we “stop and smell the roses.”
So maybe Kevin Behan’s explanation for this behavior is correct. After all, when we shake hands with strangers we can categorize them afterward and put them into our mental library, and so we won’t necessarily need to shake their hands again. And yet the first time we do engage in that ancient social ritual, it’s entirely possible that on the most basic level we’re kind of doing what dogs do when they sniff each other’s butts. We’re grounding our energy.
1) The rationale for “shaking” hands was to see if there was anything up the other guy’s sleeve, which reminds me of the famous Marx Brothers scene where the policeman is shaking Harpo’s hand and with each shake, enormous amounts of silverware keep dropping out of Harpo’s sleeve.
Interestingly, when elephants meet, they often greet each other by touching each other’s mouth with the tip of the trunk. Sometimes they’ll even grasp their trunks together, almost imitating the ancient Roman hand clasp.
In Hyenas: “Exposure of vulnerable parts to the other partner is also characteristic of hyena greetings. They stand head to tail, lift the hind quarter nearest to the partner, raise their tails, erect their penis (males) or pseudopenis (females), and sniff and lick each other’s erect “penis,” scent gland, and anus.” (Filippo Aureli, Frans B. M. Waal, Natural Conflict Resolution, 2000, p. 94)
Orca pods will approach each other in line formation and then stop about 20 meters away from one another. After a short time they swim towards each other and become extremely excited as they engage in physical caresses, swim in tight groups, and often display erections. This activity occurs when the pods first meet after the winter absence or before departing. It has also been recently associated with the presence of a sick pod member.
In Howler Monkeys: “Greetings are a conflict management mechanism used between males of similar ranks. The fission-fusion social system of this group of howlers allows males with conflicting interests to remain separated, and greetings may reduce tension during fusion events.” (“The functions of the Greeting Ceremony among male mantled howlers (Alouatta palliata) on Agaltepec Island, Mexico,” Pedro Américo D. Dias et al.)
2) Behan’s position stems from a very simple proposition (so simple you may find yourself going, “What?”). He says that the primary, bedrock environmental factor shaping the evolution of life on earth is gravity. This natural force deeply influences not only the evolution of organisms but their behavior as well (non-human and human animals alike
are always concerned, albeit unconsciously, with maintaining their physical balance). The second factor is the need to absorb energy from the environment in order to sustain life. Behan calls this “hunger” (though in my view it should also include thirst and the need to breathe). “Animal consciousness,” Behan says, “is the confluence of the two most primordial systems by which every animal functions, the primal circuits dedicated to balance and the primal circuits dedicated to hunger.” He then goes on to suggest that when dogs greet each other they’re essentially motivated by a need to “ingest” the other dog’s energy, and that smelling, which is often a precursor to eating, is the safest way to do that. (Personally, I’m still trying to “digest” that idea.)