A NOSE FOR THE JOB
Like their wild counterparts, domestic dogs have a very advanced sense of smell; indeed, they use this throughout their waking hours to make sense of the world around them. Compared with the human brain, the part of the dog’s brain devoted to smell is 40 times larger, enabling them to detect specific smells more than 1,000 times better than us. Their nose contains more than 200 million olfactory receptors, compared with our mere 5 million. This means they can detect differences in scent between not just other dogs, but people too. That is why dogs are used to detect drugs and explosives, and to find people; and why when a dog meets either another dog or a new person, it immediately sniffs them. They can even detect human emotions, such as fear or anxiety, by picking up on the scent produced by adrenaline. Their ability to recognise even subtle changes in their owner’s scent has led to them being trained as alert and support animals for people with conditions such as diabetes and epilepsy. Of all the many breeds of domestic dog, some have a better sense of smell than others: notably the bloodhound, German shepherd and beagle. It has recently been found that when they come across a new smell, dogs initially sniff using their right nostril, but once the smell becomes more familiar, they switch to using their left nostril. However, when the smell is an unpleasant one, it was found that they continued to use their right nostril to sniff it.
While cats also have an acute sense of smell, they can go one step further due to their vomeronasal, or Jacobson’s organ, located in the roof of the mouth. The cat uses this organ to analyse pheromones, which provide it with important mating, social and territorial messages. When these scents collect in its mouth, the cat uses its tongue to flick the pheromones upwards to its vomeronasal organ. As it does so, its upper lip curls, and its mouth slightly opens in a facial expression known as the flehmen response. Cat owners may have witnessed their own pets doing this.