Your dog stops dead on a walk. Nose to the ground. Won't budge. Nothing. They're in another world entirely.

And they really are.

While we humans navigate life through our eyes, dogs do it through their noses. We see the world. They smell it.

But what's actually happening when your dog sniffs? What does it look like inside that remarkable nose? How does the whole system work?

When your dog gets going, they're sniffing about five times per second. Five times. Every single second.

That's the same speed they pant at, which makes sense when you think about it. The whole system is built for rapid, efficient air processing.

Each sniffing session is a burst of activity. Usually three to ten quick inhalations and exhalations. Sometimes up to thirty if they're really interested in something.

It's not breathing. It's something else entirely.

Two Separate Airways

Dogs have two separate airways in their nose. One pathway goes straight to the lungs for breathing. The other goes up to the olfactory receptors where all the magic happens.

We have one pathway for everything. They have two.

You know those little slits on the sides of your dog's nostrils? You might never have really considered them. Most people don't. But they're crucial.

When your dog breathes out, the air doesn't come back out the front of their nose. It exits through those side slits instead.

This action means the scent molecules they've just breathed in can stay in the nose longer. They accumulate. Build up. Get analysed properly.

Meanwhile, the exhaled air creates tiny wind currents that stir up even more scent particles from the ground or the air.

"It's like a self-feeding system. Breathe in the smell. Keep it in there. Breathe out in a way that brings more smell in. Repeat."

It's like a self-feeding system. Breathe in the smell. Keep it in there. Breathe out in a way that brings more smell in. Repeat.

The Alar Fold and Independent Nostrils

There's a structure called the alar fold that makes all this possible. It's just inside the nostrils. Opens when they breathe in. Closes when they breathe out. Directs the traffic. Makes sure everything goes where it needs to go.

And perhaps most remarkably, each nostril works independently. Your dog is smelling with two separate noses that talk to different sides of the brain.

This means they can tell which nostril is picking up a scent. Which means they know which direction it's coming from.

If you really want to see a dog sniff, you need to slow down. Because it happens fast.

Researchers have used high-speed cameras to capture what's actually going on. And what they found is this: when a dog sniffs, their nostrils flare outward.

Rapidly. About five times a second. You can see it if you look closely enough.

It's different from normal breathing. The nostrils don't just open and close. They actively flare. Wider. More deliberate. More purposeful.

Head Position Tells a Story

The position of the head tells you a lot too. Nose to the ground means they're tracking something specific. Following a trail. Reading the history of who walked here, when, and where they went.

Head up in the air means they're scenting on the wind. Catching smells from further away. Gathering information about what's ahead.

Nostril Preferences in Dog Sniffing

And here's something fascinating. Dogs have preferences about which nostril they use first.

When they encounter something new or potentially threatening, they start with the right nostril. The information goes to the right side of the brain, which handles novel situations and potential danger.

If they decide the smell is safe or familiar, they switch to the left nostril. Different information. Different processing. Different response.

Your dog is literally thinking with their nose.

"So next time you're waiting while your dog sniffs that tree (and please do let them sniff, it's a welfare need for them) watch their nostrils."

So next time you're waiting while your dog sniffs that tree (and please do let them sniff, it's a welfare need for them) watch their nostrils. Watch how they move. Watch the flaring. Watch the intensity.

You're seeing one of nature's most sophisticated sensory systems in action.

Dogs have more than 100 million sensory receptor sites in their nasal cavity. We have six million. The part of their brain devoted to analysing smells is 40 times larger than ours. Forty times.

Some estimates suggest dogs can smell anywhere from 1,000 to 10,000 times better than we can. Other estimates go even higher. We're not entirely sure of the exact number, but we know it's enormous.

What the Dog Sense of Smell Can Detect

A dog can detect a teaspoon of sugar dissolved in water the size of two Olympic swimming pools.

They can smell fear because they detect the adrenaline we secrete when we're stressed. They can smell illness. Pregnancy. Emotions. Time itself, in a way, because they can tell how old a scent is.

Bloodhounds are thought to have the best noses of all dogs. But even your average family pet has abilities we can barely imagine.

The Science Behind How Dogs Sniff So Effectively

Here's something that surprised researchers. They built a 3D-printed model of a dog's nose. Tested it. Compared active sniffing to continuous breathing.

The active sniffing, that rapid in-out-in-out pattern, increased odour detection by up to 18 times compared to just breathing steadily.

Eighteen times.

The system works because of those exhaled air jets I mentioned earlier. They don't just exit passively. They actively entrain odour-laden air toward the nose. They extend the reach of the nose beyond what simple inhalation could achieve alone.

Dogs have an entire aerodynamic system designed to maximise every single sniff.

Scientists have even applied these principles to explosives detectors. Made the machines "sniff" like dogs. The improvement was 16-fold. Sixteen times better detection just by copying what dogs do naturally.

We're still learning from them.

So the next time your dog stops to sniff, remember they're reading a world you and I will never fully access. A world of information written in molecules and carried on the air.

And that deserves a bit of patience from us.

A few extra minutes on the walk, walks set up for sniffing, deliberate enrichment and scentwork.

Because for them sniffing is living!

So you are teaching your dog scentwork and want to know how you can tell when your dog recognises something? When they've found what you have put out for them? Or identified scent particles?

The Nostril Switch

The first clue is the nostril switch. You probably won't see this with the naked eye, but you might notice a change in their body language at that moment. A relaxation. A shift.

Watch the intensity of the sniffing too. When dogs are trying to work something out, the sniffs come fast and focused. Short, sharp bursts.

But when they recognise a scent, there's often a moment of satisfaction, almost. The sniffing might slow down. Become more leisurely. They've got the information they need.

Body Language Changes in Dog Sniffing Behaviour

Body language tells you loads. True scent recognition brings ease and joy. The tail wags. The body softens.

When they have successfully paired a scent with something they like, they will show happiness when they recognise it.

Head position might change as they follow particles on the air. Your dog might lift their head, look around, head towards where they expect to find the source as the particles get stronger close to that.

Individual Differences in Recognition

Research has shown that sniffing frequency actually increases with experience. The more familiar dogs become with a target scent, the faster they sniff when they encounter it. They know what they're looking for. They're more efficient at finding it.

Some dogs show what researchers call "intensive sniffing" when they're particularly focused on working out a scent puzzle. Nose down. Won't lift it. Completely absorbed. Minutes might pass.

But there's usually a moment, a visible moment, when they get it. The head comes up. The tail wags.

It's worth noting that not all dogs show their recognition in the same way. Some are subtle. A slight pause. A change in breathing. A head turned back, a check pace.

Others are dramatic. Whole body wagging. Excitement that is pretty unmissable.

Breed Differences in Dog Sniffing

Your dog's breed matters too. Scent hounds like Beagles and Bloodhounds are bred to follow scents methodically, and they'll show very focused, determined behaviour.

Gun dogs like Spaniels might be more animated when they recognise a scent they've been trained to find.

Start watching your dog on walks too, what happens when there is a squirrel? What does their nose do? What about when another dog has passed, see how they sniff the scent particles in the space the other dog was?

All of this will help you to recognise a find when your dog is searching in scentwork.

"You're not just walking a dog anymore. You're walking with a detective. A historian. An interpreter of a world you can barely imagine."

Your dog is constantly reading and recognising scents. Most of the time, you'll miss it because it happens so fast, so naturally. But if you slow down and watch, really watch, you'll start to see the patterns. The signals. The moments of recognition.

And once you can read those signs? Your walks become even more interesting. Because you're not just walking a dog anymore. You're walking with a detective. A historian. An interpreter of a world you can barely imagine.

Sniffing doesn't happen like dogs do it without being a crucial welfare need!

Dogs NEED to sniff and need the opportunity to do it on walks, just like we appreciate the view they appreciate a scent picture.

To go a step or ten further than that, why not teach your dog scentwork? It's truly amazing.

The Benefits of Scentwork

Scentwork switches on the dog's seeking system which switches off their fear system, a result that helps with reactivity.

Scentwork helps with:

• Depression
• Boredom
• Optimism
• Welfare
• Arousal
• Reactivity
• And so much more

Understanding how dogs sniff transforms your walks and opens up new ways to enrich your dog's life through their most powerful sense.

I would love you to join our community of dog guardians just like us, where we talk dog, learn and laugh a lot and generally spend time realising we are not alone in this dog life!

References

1. VCA Animal Hospitals. (n.d.). How Dogs Use Smell to Perceive the World. Retrieved from https://vcahospitals.com/know-your-pet/how-dogs-use-smell-to-perceive-the-world
2. Craven, B. A., et al. (2016). Biomimetic Sniffing Improves the Detection Performance of a 3D Printed Nose of a Dog and a Commercial Trace Vapor Detector. Scientific Reports, 6, Article 36876. https://www.nature.com/articles/srep36876
3. PubMed. (2024). Dog sniffing biomechanic responses in an odor detection test of odorants with differing physical properties. https://pubmed.ncbi.nlm.nih.gov/39569970/
4. Medical Detection Dogs. (n.d.). Sniffing. Retrieved from https://www.medicaldetectiondogs.org.uk/sniffing
5. Science Magazine/AAAS. (n.d.). The Secret of a Dog's Sniffer. Retrieved from https://www.science.org/content/article/secret-dogs-sniffer
6. Discover Magazine. (2023). Why Taking Your Dog On A "Sniffari" Will Tire Them Out More Than A Walk. https://www.discovermagazine.com/planet-earth/why-taking-your-dog-on-a-sniffari-will-tire-them-out-more-than-a-walk
7. ScienceDirect. (2024). The value of sniffing: A scoping review of scent activities for canines. https://www.sciencedirect.com/science/article/pii/S0168159124003332
8. NPR. (2016). From Fire Hydrants To Rescue Work, Dogs Perceive The World Through Smell. https://www.npr.org/2016/10/04/496417068/from-fire-hydrants-to-rescue-work-dogs-perceive-the-world-through-smell
9. Siniscalchi, M., et al. (2016). The dog nose "KNOWS" fear: Asymmetric nostril use during sniffing at canine and human emotional stimuli. Applied Animal Behaviour Science, 194, 62-66. https://www.sciencedirect.com/science/article/abs/pii/S0166432816300699
10. Scientific American. (2015). What You Don't Know About Your Dog's Nostrils. https://blogs.scientificamerican.com/dog-spies/what-you-don-t-know-about-your-dog-s-nostrils/