How long should a dog take sniffing on a walk?
A friend asked me an interesting question last week: how long should he allow his dog to stop and sniff an area? He explained that when he takes his dog for walks, she often pauses, sniffing around in a particular spot. She might carry on doing this for two or three minutes, or even longer.
Meanwhile, he's standing around, getting cold, and wondering when it would be fair to tug her leash and encourage her to move on. He wanted me to tell him what was going on in her head, and how should he deal with her?
Dog behaviour is often intriguing and difficult to understand. Obviously, they can't talk to us, so we just have to make the best possible guess at what's going through their head.
So when this dog is sniffing an area, what is she thinking? To answer this properly, it's worth reviewing what we know about dogs and sniffing.
The sense of smell of a dog is far, far richer than our own: three aspects of their anatomy reveal the reasons for this.
First, an average dog has between 125 and 250 million scent receptors in the lining of the nose. Humans only have around 5 million.
Second, the part of the brain dedicated to processing scents (the "olfactory lobe") is 40% bigger in dogs than in humans. The part of the brain that deals with vision is bigger in humans compared to dogs, because seeing is more important to smelling for us.
Third, the moist surface of the tip of a dog's nose acts as a landing pad to catch the molecules in an odour, allowing the scent receptor sites deeper in the nose to process them.
And fourth, the internal structure of a dog's nose is designed to allow pockets of air to linger over specialised densely innervated areas, allowing maximal extraction of information from the scent particles. In humans, the air goes in and out rapidly, without pausing in pockets like this.
These differences give a dog an astonishingly sensitive sense of smell. It has been said that a dog has a sense of smell that is between 10000 and 100000 more sensitive than humans. To put this into context, if a similar comparison was made to vision, using the lower figure, if a human could see something 500 metres away, a dog would be able to see something 5000 kilometres away. This gives you an idea of their remarkable ability to pick up subtle odours.
To give another comparison, while a human would notice if a cup of coffee had had a teaspoon of sugar added to it, a dog could detect a teaspoon of sugar in two Olympic-sized swimming pools.
There are many examples of the impressive feats that dogs can accomplish using their sense of smell. Smelling buried items up to twelve meters underground. Detecting human fingerprints that are a week old. If you throw a small pebble as far as you can on a pebble-filled beach, they are able to find it and bring it back to you.
And this sense of smell can be harnessed by humans who train dogs. Everyone has heard of drug-sniffing dogs at ports and airports, dogs being used to track people, to detect victims buried in earthquakes and to sniff out truffles in woodland.
More recently, dogs have been used to carry out diagnostic tests on urine samples from humans: they can sniff out prostate and bladder cancer cells, providing more accurate diagnoses than any human-designed technology. They have also been shown to detect lung and breast cancer cells by sniffing patients' breath.
So it's obvious that dogs experience an entirely different world of smells compared to humans. Which brings us back to my friend's dog sniffing in a patch of undergrowth.
What would be going on inside that dog's head? The area is popular for dog walking, and over the previous few days, hundreds of dogs will have passed by that spot. It is quite possible that my friend's dog could be picking up the individual odour of every single dog. To make a comparison, it could be like you or I scanning a group of people, seeking out friends in a crowd.
It's also possible that the process of sniffing areas like this might in itself bring pleasure to the dog, perhaps like a human gazing at an intriguing picture in an art gallery, or someone listening to a song that they enjoy.
So how long should the dog be left sniffing?
The best answer is probably to follow through with those comparisons.
How long should someone be left to look at a picture in an art gallery before being asked to move along? The answer is "as long as they want to keep looking". For as long as they continue to gaze at the picture, they are obviously enjoying the sight of the work of art.
And how long should someone be left listening to a song? The answer is "as long as they want to keep listening". Nobody wants to have the radio turned off in the middle of an enjoyable piece of music. Nobody wants to be dragged away from music while they are still appreciating the sound.
And so it is for dogs sniffing in undergrowth. Give them as long as they want. Wrap up warmly so that you don't mind waiting around, and let them have a drawn-out, lengthy, indulgent, deep inhalation. It's one of their favourite pastimes, so don't rush them off. Take a long pause, and let them enjoy those sniffing sensations.