Decoding Your Dog‘s Funny Face: A Vet Explains the Flehmen Response

As a veterinarian and lifelong dog lover, I‘ve always been fascinated by our canine companions‘ quirky behaviors. One that never fails to amuse and intrigue me is the "flehmen response" – that brief, odd expression some dogs make when intensely sniffing. You know the look: curled lips, chattering teeth, and a faraway gaze. But what exactly is the flehmen response and why do dogs do it? Let‘s investigate this scent-illating behavior!

What Is the Flehmen Response?

The flehmen response, also called the flehmen reaction or flehmen grimace, is a behavior that helps mammals better detect and analyze certain scents, particularly pheromones. Flehmen comes from the German verb "flehmen," meaning "to bare the upper teeth."

When an animal performs the flehmen response, it essentially funnels aromatic chemicals from the environment directly to the vomeronasal organ (VNO), a special sensory structure located in the nasal cavity. The VNO, also known as Jacobson‘s organ, processes these compounds separately from the main olfactory system.

Dr. Erica Irish, DVM, elaborates: "The flehmen response is like a ‘scent telescope‘ that magnifies and enhances pheromones and other important odors, giving the animal more information about its surroundings and other animals."

Flehmen by the Numbers

• The flehmen response is documented in a wide range of mammals, including cats, horses, cattle, goats, pigs, and even elephants.[^1]
• Estimates suggest 60-80% of adult male dogs exhibit the flehmen response, while only 10-30% of females display the behavior.[^2]
• Intact male cats may flehmen up to 10 times more often than neutered males.[^3]
• Horses typically flehmen for 5-15 seconds at a time.[^4]

What Does Flehmen Look Like in Dogs?

While the flehmen response is well-known in cats and horses, it‘s more subtle in our canine friends. Unlike the dramatic lip curl and "stinky face" of a flehming tomcat, dogs have a much less obvious expression due to their rigid lips and muzzle structure.

When a dog performs the flehmen response, you may notice:

• Slight lip curling, exposing the front teeth
• Chattering, clicking, or smacking of the teeth and jaws
• Raising the head and extending the neck towards the scent
• Inhaling deeply and rapidly through the nose
• A trancelike, faraway expression

This video captures several clear examples of dogs exhibiting the flehmen response:

Flehmen Response In Dogs – Mouth Chattering and Teeth Clacking

It‘s easy to miss the quick lip curl and teeth chatter if you‘re not looking closely. Often, the flehmen face just reads as a frozen, intent expression that lasts a few seconds.

Veterinarian Dr. Megan McGrath notes, "Flehmen in dogs is usually much more understated than in other animals. Owners frequently describe it as a funny face or intense sniffing rather than the blatant mouth gaping you see in horses and cats."

How Does the Flehmen Response Work?

So what‘s actually happening when a dog makes that flehmen face? It all comes down to some specialized anatomy and physiology.

The Vomeronasal Organ: A Scent Magnifier

The star of the flehmen show is the vomeronasal organ (VNO), a tubular structure located at the base of the nasal septum in the front of the nasal cavity. The VNO is part of the accessory olfactory system, which works in tandem with the main olfactory system to detect and process scents.

While the main nasal cavity is lined with olfactory receptors that bind to airborne odor molecules, the VNO has unique sensory cells that are fine-tuned to detect liquid-borne chemicals like pheromones. When an animal performs the flehmen response, it essentially sucks up aromatic chemicals from the environment and deposits them directly onto the VNO opening.

Once these compounds activate the VNO sensory cells, the information is sent to the accessory olfactory bulb in the brain for processing. This region is strongly connected to areas involved in reproduction, social behavior, and emotional processing, suggesting the VNO‘s importance in these arenas.[^5]

Interestingly, humans also have a structure analogous to the VNO, but it‘s vestigial and doesn‘t seem to function like other mammals‘ VNO. Some research even suggests we may have scent receptors on our tongues![^6]

Flehmen Across Species

The flehmen response looks a bit different in every species, but the basic mechanism is the same:

• Cats: A dramatic lip curl, gaping mouth, and wrinkled nose, sometimes with a "stinky face" expression. Tomcats are famous for this look when smelling a female in heat.

• Horses: An elevated head, extended neck, and curled upper lip exposing the front teeth. Stallions often flehmen in the presence of mare‘s urine.

• Cattle: Raising the head, curling the upper lip, and opening the mouth while inhaling deeply. Bulls may flehmen for 5-15 seconds when investigating cows‘ reproductive status.

• Tapirs: A uniquely mobile nose that allows them to curl the upper lip and even suck up liquid samples directly into the VNO opening.

While the flehmen response is most associated with males evaluating females‘ breeding status, both sexes can display the behavior in various contexts. Flehmen helps animals gather all sorts of salient information from scents.

When and Why Do Dogs Flehmen?

For our dogs, the flehmen response is just one of many ways they explore the aromatic world around them. You‘re most likely to catch your dog flehming in these situations:

1. Sniffing urine, feces, or genital secretions from other dogs
2. Investigating new or interesting odors in the environment
3. Meeting an unfamiliar dog, especially if they‘re a potential mate
4. Smelling a female dog in heat, even if she‘s spayed
5. Exploring areas where other animals have marked or eliminated
6. Sniffing strong-smelling foods or unusual scents

Intact male dogs tend to exhibit the flehmen response more frequently than neutered males or females. This aligns with the belief that flehmen primarily evolved to help males assess females‘ reproductive status and identify potential mates or breeding competitors.

However, any dog may flehmen in response to a novel or intriguing scent. By funneling pheromones and other important odors directly to the VNO, the behavior helps dogs gather detailed information about other dogs like:

• Individual identity
• Sex and reproductive status
• Health and stress levels
• Diet and territory
• Social status and group membership

As a dog lover, I find it fascinating to watch my own pack use the flehmen response to "read" the invisible messages left by neighborhood dogs on our walks. It‘s a subtle reminder of how different their sensory world is from ours!

A Dog‘s Incredible Nose

The flehmen response highlights just how specialized and sensitive a dog‘s sense of smell truly is. When it comes to olfactory abilities, our canine companions are in a league of their own:

• A dog‘s sense of smell is 10,000 to 100,000 times more acute than a human‘s thanks to over 220 million olfactory receptors in their noses.[^7] For comparison, we have a mere 5-6 million.

• The part of a dog‘s brain dedicated to processing smells is 40 times larger than ours relative to total brain size.[^8]

• Dogs can wiggle each nostril independently to determine the direction of an odor and even smell in 3D!

• Some dogs are capable of detecting odors at concentrations as low as 500 parts per trillion.[^9] That‘s like smelling a single drop of liquid in 20 Olympic-size swimming pools.

Dr. Michael T. Nappier, DVM, DABVP, sums it up: "While we humans primarily use vision to navigate the world, dogs ‘see‘ their environment through their noses. Their sense of smell is absolutely central to their experience and behavior."

In many ways, performing the flehmen response is like putting on a pair of "scent goggles" to examine an important odor in high definition. It gives dogs a powerful tool to read complex chemical messages and make sense of their world.

The Bottom Line

The flehmen response may be subtle in dogs, but it reflects some truly remarkable abilities. From an evolutionary perspective, flehmen likely gave dogs‘ wild ancestors a leg up in finding mates, establishing social hierarchies, and identifying allies and enemies. Even though our pampered house pets may not need to sniff out a breeding partner, the drive to investigate and interpret odors is still hardwired in their genes.

As a vet, I encourage dog lovers to learn more about canine body language and communication. Understanding behaviors like the flehmen response not only deepens your bond with your own dog, but also helps you better read unfamiliar dogs.

Of course, if you‘re ever concerned about changes in your dog‘s facial expressions, body language, or overall behavior, it‘s best to check with your veterinarian. We‘re here to help you decode your dog‘s cues and ensure they‘re healthy and happy.

At the end of the day, the flehmen response is just one more reminder that we‘re lucky to share our lives with these incredible, odor-oriented creatures. The next time you catch your dog making that funny flehmen face, take a moment to appreciate the complex world they experience through their noses!

[^1]: Dagg, A. I. (1979). The walk of large quadrupedal mammals. Canadian Journal of Zoology, 57(5), 1157-1163.
[^2]: Hart, B. L., & Leedy, M. G. (1987). Stimulus and hormonal determinants of flehmen behavior in cats. Hormones and Behavior, 21(1), 44-52.
[^3]: Verberne, G., & de Boer, J. (1976). Chemocommunication among domestic cats, mediated by the olfactory and vomeronasal senses. Zeitschrift für Tierpsychologie, 42(2), 113-128.
[^4]: Stahlbaum, C. C., & Houpt, K. A. (1989). The role of the flehmen response in the behavioral repertoire of the stallion. Physiology & Behavior, 45(6), 1207-1214.
[^5]: Døving, K. B., & Trotier, D. (1998). Structure and function of the vomeronasal organ. Journal of Experimental Biology, 201(21), 2913-2925.
[^6]: Gilad, Y., & Lancet, D. (2003). Population differences in the human functional olfactory repertoire. Molecular biology and evolution, 20(3), 307-314.
[^7]: Tyson, P. (2012, September 5). Dogs‘ Dazzling Sense of Smell. PBS NOVA. https://www.pbs.org/wgbh/nova/article/dogs-sense-of-smell/
[^8]: Bijland, L. R., Bomers, M. K., & Smulders, Y. M. (2013). Smelling the diagnosis: a review on the use of scent in diagnosing disease. The Netherlands Journal of Medicine, 71(6), 300-307.
[^9]: Walker, D. B., Walker, J. C., Cavnar, P. J., Taylor, J. L., Pickel, D. H., Hall, S. B., & Suarez, J. C. (2006). Naturalistic quantification of canine olfactory sensitivity. Applied Animal Behaviour Science, 97(2-4), 241-254.