A dog's sense of smell is so sensitive, it could almost be described as a superpower. Indeed, if our eyesight was as sensitive as a dog's nose is to smell, we'd be able to see an object 3,000km away - perfectly!
It's well known that dogs can be trained to detect illicit substances through masking smells such as coffee or paraffin, so what's to stop them smelling food in your stomach?
Actually, the answer is very little! Yes, they probably could detect food that has been recently eaten, if trained to do so. However, the human body is not a static thing and once the food is in the stomach, it starts to change as it is digested. As stomach acids digest the food, so it's scent signature will change and, like smoke that dissipates on the wind, the scent will no longer be there to detect.
Signs a Dog can Smell Food in Your Stomach
Dogs follow a scent in a particular way. If the dog was trained to detect a certain food, then they will start by casting the net widely in order to pick up on any scent molecules in the air.
This involves the dog moving rapidly from side to side, taking lots of rapid shallow sniffs as they go. This is to sample the air and work out where the smell is strongest.
The dog then moves along the path of the strongest smell, sniffing as they go. As the scent becomes localized to an area, the dog slows down to survey the air in more detail. They may even stop moving and hold their head up to scent the air or stick their nose to the ground. They then take fewer breaths that are much deeper, in order to best process the scent molecules they encounter.
As the dog slowly moves towards the substance they are trained to detect, they will signal a 'find' in different ways. Some dogs are trained to howl up a storm in order to draw their handler's attention. Whilst other dogs are trained to drop quietly to the ground and lie still, so as to alert the handler but no-one else as to their find.
History of Dogs and Their Sense of Smell
Early man was a hunter-gatherer, rather than a farmer. They had need of an animal that could track another to take the hunter to his prey. So much the better if that tracking dog could also protect them and bark to guard the camp. The final puzzle piece that ensured the success of dogs as companions for people, is their eagerness to please their master.
Thus the story of dogs and mankind is intimately interwoven. As mankind developed and started farming, so they had a need for dogs that could herd. As people began to realize they could breed dogs to produce specific, highly-desirable traits such as the ability to guard, track, or protect, so various dog breeds developed.
One branch of this development is the scent hounds. These dogs have been bred with an emphasis on their sense of smell. They were largely used for hunting, but in the 20th century, a new use was discovered for their awesome ability to follow a scent trail.
In the 1940s, the American military trained dogs to sniff out unexploded landmines in North Africa. The result was such a success that it saved many lives. Moving forward from this, the potential to detect substances from smuggled cash to illegal substances and more, was uncovered.
By the 1960s and 1970s, sniffer dogs were regularly used to find illegal drugs and explosives. More recently, dogs have been trained to pick up subtle smells linked to cancer in people, or even dangerously low blood sugar levels in diabetics.
The Science of How Dogs Scent
Dogs have a better sense of smell than people. Indeed, some dog breeds have a better sense of smell than others. This is down to the selective development of the canine nose and the scent-processing centers in the brain.
For example, inside the nasal cavity of the dog are ultra-fine scrolls of bone, which is lined with a scent-sensitive moist membrane. The surface area of this membrane is mind-bogglingly big, especially compared to humans', and it represents the superior detecting ability to pick up and capture individual scent molecules. Thus, even if a smell is very faint, the dog has a better chance of picking it up.
Then, once scent molecules have interacted with that mucous membrane, messages are passed to the olfactory (scent) center in the brain. Again, in the scenting breeds, this processing area is many times larger than the similar region in the human brain, which gives the dog a superior ability to process and interpret those signals.
And last but not least, is the actual canine nose - that leathery, black button so characteristic of dogs. The fact that it is usually slightly moist is another way of trapping scent molecules so they can be inhaled into the nose and then processed.
Training a Dog to Track Scents
Yes, a dog could smell freshly swallowed food in your stomach, but they'd need to be trained in order to tell a handler about their find. This is done using classic drug detection training methods.
To start, you need to select a dog that has a good nose and a strong play drive. The latter is so that you have a means of incentivizing and rewarding the dog.
Start by having an enthusiastic game of tug with a clean towel that has no odor. Then, rub the towel with a little of the food substance you want the dog to detect. Now, play tug again.
For the next step, offer the dog a choice of two towels: One unscented and the other having a subtle food odor. If the dog selects the clean towel, you ignore them and don't play. However, if they choose the foody-towel, they are praised and rewarded with a game of tug.
Moving on, offer several towels, of which only one is scented. Reward the dog only when they choose the foody one. And finally, once the dog is regularly selecting the correct towel by scent, place the towel out of eyeline and encourage the dog to find it using their nose. And, presto - a dog trained to scent out a certain food.
By Pippa Elliott
Published: 06/06/2018, edited: 04/06/2020