To understand your dog – you must understand his nose. As a human being you understand and interact with the world around you predominantly by sight – your dog defines the world and his place in it through his sense of smell.
Alexandra Horowitz is a canine cognition researcher at Bernard College. In her book, Inside of a Dog, she gives a great analogy of comparing our sense of smell to our dogs:
Pour a cup of coffee – take a good smell. Now add 1 teaspoon of sugar – can you notice the scent change? Now imagine what the world is like for your dog because he can detect a teaspoon of sugar in a million gallons or 2 Olympic sized swimming pools filled with water.
Sniffing and breathing are two separate functions for a dog; when dogs take those short little sniffs, they are actually saving some of the scent for analysis. When we inhale , smelling and breathing both follow the same pathway through our nose. When dogs inhale, a bit of tissue inside their nose separates the flow into two distinct pathways, one for olfaction (scent) and one for respiration.
When the dogs sniff, about 12 percent of the air gets redirected into a recessed part of their nose which is specifically designed to analize scent; the scent filters through a maze of tiny bones called turbinates. Brent Craven, a bioengineer at Pennsylvania State University, and his team found that the maze separates the odour molecules based on the different chemical properties. The receptors that are inside the tissue lining of the turbinates, then recognises the scent molecules by shape and size – sending the appropriate signals to the brain.
The olfactory receptors (or scent glands) in your dogs nose greatly outnumber a humans. We have about 6 million, whereas a dog can have as many as 300 million depending on breed. Also the part of his brain which analyises smell is proportionally 40 times greater than ours. This allows your dog to detect odours in parts per trillion.