Would you like to know some random facts about a dog's nose?
[Whenever] we exhale, we purge the odorants from our noses, causing our experience of smell to strobe and flicker. Dogs, by contrast, get a smoother experience because odorants that enter their noses tend to stay there, and are merely replenished by every sniff.
The shape of their nostrils adds to this effect. If a dog is sniffing a patch of ground, you might imagine that every exhalation would blow odorants on the surface away from the nose. But that's not what happens. The next time you look at a dog's nose, notice that the front-facing holes taper off into side-facing slits. When the animal exhales while sniffing, air exits through those slits and creates rotating vortices that waft fresh odors into the nose. Even when breathing out, a dog is still sucking air in. In one experiment, an English pointer (who was curiously named Sir Satan) created an uninterrupted inward airstream for 40 seconds, despite exhaling 30 times during that period.
With such hardware, it's no wonder that dog noses are incredibly sensitive. But how sensitive? Scientists have tried to find the thresholds at which dogs can no longer smell certain chemicals, but their answers are all over the place, varying by factors of 10,000 from one experiment to another. Rather than focusing on these dubious statistics, it's more instructive to look at what dogs can actually do. In past experiments, they have been able to tell identical twins apart by smell. They could detect a single fingerprint that had been dabbed onto a microscope slide, then left on a rooftop and exposed to the elements for a week. They could work out which direction a person had walked in after smelling just five footsteps. The've been trained to detect bombs, drugs, landmines, missing people, bodies, smuggled cash, truffles, invasive weeds, agricultural diseases, low blood sugar, bedbugs, oil pipeline leaks, and tumours.
Migaloo can find buried bones at archeological sites. Pepper uncovers linger oil pollution on beaches. Captain Ron detects turtle nests so that the eggs can be collected and protected. Bear can pinpoint hidden electronics, while Elvis specializes in pregnant polar bears. Train, who flunked out of drug detection school for being too energetic, now uses his nose to track the scat of jaguars and mountain lions. Tucker used to hang off the bow of boats and sniff for orca poop; he has since retired, and his duties now fall to Eba. If it has a scent, a dog can be trained to detect it.
From "An Immense World: How Animal Senses Reveal the Hidden Realms Around Us", by Ed Yong.
[Replaced quoted italics with bold because quotes here won't let me use another form of emphasis.]