A dog has around 200 million sensitive cells in its nose compared to a human’s five million, so its sense of smell is around 40 times better than ours.
A dog’s sense of smell is made even stronger by an organ in the roof of the mouth that humans do not possess. This enables it to ‘taste’ a smell, turning a weak smell into a stronger one.
This sensitivity to smell, especially butyric acid emitted in sweat, enables a dog to pick out the ball belonging to its owner from several balls thrown by different people. It also enables Bloodhounds to track an escaping convict up to 100 miles.
Trained dogs can also detect the odours of heroin, marijuana and cocaine hidden in suitcases even if surrounded by something strong smelling such as perfume. Other dogs can be trained to detect the acid in nitroglycerine and the sulphur in gunpowder for work with explosives.
Dogs are even used to sniff out truffles in the ground. Some believe their sense of smell makes them suitable for infra-red detection, which helps them find humans in snowdrifts.
A dog, however, is not so sensitive to some smells that humans regard as important, such as the smell of cooking or flowers. A dog doesn’t water at the mouth when a roast joint sizzles in the oven, nor does it get much pleasure from the smell of a rose.
Thinking that a dog does appreciates these things is another sign of anthropomorphism but that is another subject.