Your dog smells you -- better than you think

One of the cheeriest genres of YouTube video compilations is that of dogs greeting soldiers returning home.

Whether their owner's deployment was long or short, the dogs erupt into that singular, irrepressible doggy celebration: bounding, tails wagging maniacally, rolling on their backs, whimpering and grinning, weaving between the soldier's legs. There is little doubt that the dogs remembered, loved and missed their people.

In some of the videos, though, this recognition is at first in doubt: As the (often-uniformed) person arrives or enters the home, the dog barks, approaching guardedly, tail down and ears back. They do not know this person.

But then comes a magical moment of transformation. Watch the nose. Each dog lifts his nose in the air, catching a whiff on the breeze. Or sniffs one offered hand, then the other. In an instant, the stranger is transformed -- into the person the dog knows and longed to see.

We all know that dogs are good at smelling. Just how good has only recently come to light.

The world, to a dog, is wrought of smells. As we see images in our minds, he glimpses scents; as we speak in words, he communicates in fumes. I've spent the past few years studying how pet dogs use their noses and watching working dogs be trained to detect scents.

Enabled by their cooperativeness and responsiveness with people, dogs are now earning a reputation for their scent-detection work. No less than the U.S. Supreme Court described the detector dog's sniff as "sui generis", a tool unlike any other.

Every visitor to an airport sees explosive-detection dogs; cross a border and you'll meet a drug dog sniffing at your tires. Police dogs are ubiquitous. But detection dogs (known in various dog circles as sniffer dogs, detector dogs, or working dogs) detect much more than explosives and drugs. The limit of application of the dog nose to finding something is thus far defined more by the limit of our imagination than by its ability.

Our imagination has proven much more fertile of late. To date, dogs have been trained to detect not just explosives, but landmines and accelerants. By smell alone, dogs find illegally imported guava, illicit cell phones in prison, imported shark fins in suitcases, termites, fire ants and bed bugs.

Some dogs smell for environmental contaminants at industrial waste sites, and others find the smuggled tusks and horns unfairly removed from their elephant and rhinoceros hosts.

By scat alone, dogs can pinpoint the hard-to-find Puget Sound orca; track populations of black bears, bobcats, and bush dogs; they gather data on bird strikes in wind farms and dairy cows in estrous. There are now dogs detecting their owners' falling glucose levels and imminent seizures; others have sniffed out cancer volatiles on peoples' skin, urine, and breath.

Provided there is an odor (and just about every substance has one), dogs seem to have the ability to smell out almost anything. Thus, dogs detect us. Tracking, trailing, search-and-rescue, and scent-identification dogs pursue the missing, escaping, lost or dead -- the criminal, confused, unseen or unlucky.

The smell of person is so strong that dogs can follow it over time, through water, after the person is long gone, and even after the thing the person touched has actually blown up. In one study, researchers found trained bloodhounds able to identify who had touched a pipe bomb -- after the pipe bomb exploded.

Dogs have been trained to find drowned people. The odor of decomposition rises to the surface of a lake or other still body of water and some dogs can even track in flowing stream or river water.

Avalanche-rescue dogs have found people buried under 24 feet of snow: The person's scent travels to the surface and the dog, after some digging, alerts there. In the Netherlands, Germany, Poland and other countries, courts have sanctioned evidence from scent-identification lineups.

To your dog, you are your scent. By constant exposure to each other, you are essentially training dogs on the particular bouquet of you, which is a special mix of oleic, palmitic and stearic acids; they can notice if any of the ingredients in the mix are a few micrograms more or less.

Research with one very cooperative fox terrier found that she could detect one milligram of butyric acid -- think smelly socks -- among 100 million cubic meters of air.

You'll notice your spouse's smelly socks the moment after they are removed in the bedroom: That's around 40 cubic meters of very socky-smelling air. The dog knows if someone's removed his socks in a room bigger than the gargantuan vehicle assembly building at NASA's Kennedy Space Center in Florida, made to put the space shuttles together.

So any dog in the 3.7 million cubic meters of Space Center would be alert to sweaty astronauts.

Given their sensitivity to the presence, absence, or change of an odor, dogs essentially smell time passing. The past is underfoot; the odors of yesterday have come to rest on the ground. And here, too, smell gives pet dogs a message about their owners.

The odors we leave around our homes when we leave lessen reliably as the day wears on. As we are gone, our home smells less of us. If we were able to sneak one of our well-used gym shirts into our homes halfway through the day, we might succeed in resetting the dog's clock as to when to expect us home (thus surprising the dog when we do arrive, as a Nova showdemonstrated with one dog and his owners).

Knowing the importance of smells in general -- and my smell, in particular -- to my dogs has changed our lives together. In the morning they sniff me awake; I let them lick (a way for them to absorb molecules for smelling). When I return home from a trip, I reach down to greet them -- and let them smell me back. Now I even take a sniff of them myself. What I would do to see the world they smell.