(CNN)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.
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 show demonstrated 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.