First sniff of the day: Pump wanders into the living room in the morning while I am dishing out her food. She's looking sleepy but her nose is wide awake, stretching every which way as though doing morning exercises. She reaches her nose toward the food without committing her body, and sniffs. A look at me. Another sniff. A judgment has been levied. She backs from the bowl and forgives me by nosing my outstretched hand, her whiskers tickling while her moist nose examines my palm. We go outside and her nose is gymnastic, almost prehensile, happily taking in smells that gust by...
We humans tend not to spend a lot of time thinking about smelling. Smells are minor blips in our sensory day compared to the reams of visual information that we take in and obsess over in every moment. The room I'm in right now is a phantasmagoric mix of colors and surfaces and densities, of small movements and shadows and lights. Oh, and if I really call my attention to it I can smell the coffee on the table next to me, and maybe the fresh scent of the book cracked open--but only if I dig my nose into its pages.
Not only are we not always smelling, but when we do notice a smell it is usually because it is a good smell, or a bad one: it's rarely just a source of information. We find most odors either alluring or repulsive; few have the neutral character that visual perceptions do. We savor or avoid them. My current world seems relatively odorless. But it is most decidedly not free of smell. Our own weak olfactory sense has, no doubt, limited our curiosity about what the world smells like. A growing coalition of scientists is working to change that--and what they have found about olfactory animals, dogs included, is enough to make us envy those nose-creatures. As we see the world, the dog smells it. The dog's universe is a stratum of complex odors. The world of scents is at least as rich as the world of sight.
...Her ungulate-grazing sniff, nose deep in a patch of good grass, trawling the ground and not coming up for air; the examinatory sniff, judging a proffered hand; the alarm-clock sniff, close enough to my sleeping face to tickle me awake with her whiskers; the contemplative sniff, nose held high in the wake of a breeze. All followed by a half-sneeze--just the CHOO, no AH--as though to clear her nostrils of whatever molecule she'd just inhaled...
Dogs don't act on the world by handling objects or by eyeballing them, as people might, or by pointing and asking others to act on the object (as the timid might); instead, they bravely stride right up to a new, unknown object, stretch their magnificent snouts within millimeters of it, and take a nice deep sniff. That dog nose, in most breeds, is anything but subtle. The snout holding the nose projects forth to examine a new person seconds before the dog himself arrives on the scene. And the sniffer is not just an ornament atop the muzzle; it is the leading, moist headliner. What its prominence suggests, and what all science confirms, is that the dog is a creature of the nose.
The sniff is the great medium for getting smelly objects to the dog, the tramway on which chemical odors speed up to the waiting receptor cells along the caverns of the dog nose. Sniffing is the action of inhaling air, but it is more active than that, usually involving short, sharp bursts of drawing air into the nose. Everyone sniffs--to clear the nose, to smell dinner cooking, as part of a preparatory inhale. Humans even sniff emotively, or meaningfully--to express disdain, contempt, surprise, and as punctuation at a sentence's end. Animals mostly sniff, as far as we know, to investigate the world. Elephants raise their trunk into the air in a "periscope sniff"; tortoises slowly reach and open their nostrils wide in a sniff; marmosets sniff while they nuzzle. Ethologists watching animals often take note of all these sniffs, for they may precede an attempt to mate, a social interaction, aggression, or feeding. They record an animal as "sniffing" when it brings its nose close to--but not touching--the ground or an object, or an object is brought close to--but not touching--the nose. In these cases, they are assuming that the animal is in fact inhaling sharply--but they may not be able to get close enough to the animal to see the nostrils moving, or the tiny vortex of air that stirs the area in front of the nose.
Few have looked closely at exactly what happens in a sniff. But recently some researchers have used a specialized photographic method that shows air flow in order to detect when, and how, dogs are sniffing. They have found that the sniff is nothing to be sniffed at. In fact one could make the case that it is neither a single nor a simple inhalation. The sniff begins with muscles in the nostrils straining to draw a current of air into them--this allows a large amount of any air-based odorant to enter the nose. At the same time, the air already in the nose has to be displaced. Again, the nostrils quiver slightly to push the present air deeper into the nose, or off through slits in the side of the nose and backward, out the nose and out of the way. In this way, inhaled odors don't need to jostle with the air already in the nose for access to the lining of the nose. Here's why this is particularly special: the photography also reveals that the slight wind generated by the exhale in fact helps to pull more of the new scent in, by creating a current of air over it.
This action is markedly different from human sniffing, with our clumsy "in through one nostril hole, out through the same hole" method. If we want to get a good smell of something, we have to sniff-hyperventilate, inhaling repeatedly without strongly exhaling. Dogs naturally create tiny wind currents in exhalations which hurry the inhalations in. So for dogs, the sniff includes an exhaled component that helps the sniffer smell. This is visible: watch for a small puff of dust rising up from the ground as a dog investigates it with his nose.
Given our tendency to find so many smells disgusting, we should all celebrate that our olfactory system adapts to an odor in the environment: over time, if we stay in one place, the intensity of every smell diminishes until we don't notice it at all. The first smell of coffee brewing in the morning: fantastic...and gone in a few minutes. The first smell of something rotting under the porch: nauseating...and gone in a few minutes. The sniffing method of dogs enables them to avoid habituation to the olfactory topography of the world: they are continually refreshing the scent in their nose, as though shifting their gaze to get another look....