Why do cats open their mouth when they smell?

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Cats are fascinating creatures with unique behaviors and instincts that have been studied for centuries. One intriguing behavior that many cat owners may have noticed is the way their cats open their mouths when they smell something interesting. This behavior can be confusing to some cat owners, as it seems counterintuitive for an animal to open their mouth while smelling. However, there are scientific reasons behind this behavior that shed light on the incredible sense of smell that cats possess.

In this article, we will explore the reasons why cats open their mouth when they smell and discuss the various factors that may influence this behavior. By understanding more about cat behavior and their sense of smell, we can deepen our appreciation for these beloved pets and provide better care for them.

The Science Behind Cat Smelling Behavior

Cats are known for their keen sense of smell, which is essential to their survival in the wild. Their sense of smell is far superior to that of humans and is critical for navigation, hunting, and communication. The anatomy of a cat’s nose plays a significant role in its sense of smell.

Cats have a specialized organ called the Jacobson’s organ or vomeronasal organ (VNO), located in the roof of their mouth, which is responsible for detecting pheromones. When a cat smells something of interest, they often make a distinctive face called the Flehmen response. This involves opening their mouth slightly, pulling back their lips, and curling their tongue. This behavior helps the cat to transfer scents to the VNO, which is located near the roof of the mouth and enhances its ability to detect pheromones.

The VNO is connected to a part of the brain called the accessory olfactory bulb, which is responsible for processing pheromones. This allows cats to detect a wide range of chemical signals, such as those released by potential mates, prey, and territorial markings left by other cats. In fact, studies have shown that cats can detect odors at concentrations as low as one part per million, making their sense of smell incredibly powerful.

In addition to the VNO, cats have a highly sensitive olfactory epithelium, which lines the nasal cavity and contains millions of olfactory receptor cells. This allows cats to detect a wide range of odors, including those that are imperceptible to humans. As they inhale, the air passes over the olfactory epithelium, which helps to detect and identify different smells.

Overall, the sense of smell plays a crucial role in a cat’s life and is an essential tool for communication, hunting, and navigating their environment. The anatomy of their nose and specialized organs like the VNO allow them to detect and identify a wide range of odors, making them highly skilled hunters and adaptable creatures.

The Open Mouth Behavior in Cats

One behavior that can be observed in cats when they encounter an interesting scent is opening their mouth slightly. This behavior is known as the Flehmen response and is often accompanied by a curled tongue and pulled-back lips. It may seem strange that a cat would open their mouth when smelling, as humans typically close their mouths to enhance their sense of smell. However, this behavior serves an important purpose for cats.

When a cat smells something of interest, it may open its mouth to draw in more air and get a better scent of the object. The air is then directed to the VNO, which is responsible for detecting pheromones. The Flehmen response is particularly important for detecting pheromones, as these chemical signals are often found in concentrated areas such as urine and feces. By opening their mouth, cats can better detect and identify these scents.

In addition to enhancing their sense of smell, the Flehmen response may also help cats to analyze the object they are smelling. By curling their tongue and pulling back their lips, cats can direct the scent toward the VNO, which allows them to analyze the chemical makeup of the odor. This can provide valuable information to the cat, such as the sex, age, and reproductive status of another cat.

It’s worth noting that not all cats exhibit the Flehmen response, and it may be more common in males than females. Additionally, some cats may only exhibit the behavior in response to certain scents or objects. Overall, the open-mouth behavior in cats is a unique and fascinating behavior that serves an important purpose in their sense of smell and analysis of their environment.

Other Factors that Affect Cat Smelling Behavior

While the open-mouth behavior in cats is primarily associated with their sense of smell, there are several other factors that can influence a cat’s smelling behavior.

  1. Mood: Just like humans, cats can be affected by their mood and emotional state. If a cat is feeling stressed, anxious, or upset, it may be less interested in exploring its environment and less likely to exhibit the Flehmen response.
  2. Age: As cats age, their sense of smell may decline. Older cats may not be as interested in exploring their environment or may have difficulty detecting certain scents.
  3. Health: Certain health conditions can affect a cat’s sense of smell. For example, a respiratory infection or nasal congestion can make it difficult for a cat to smell properly. Additionally, some medications can affect a cat’s sense of smell.
  4. Genetics: Some cats may be genetically predisposed to certain smell preferences. For example, some breeds of cats may be more interested in exploring outdoor scents, while others may prefer indoor smells.
  5. Training: Cats can be trained to recognize and respond to certain smells, such as the smell of their owner or a specific food. This can influence their smelling behavior and may lead to a stronger or more focused response to certain scents.

Overall, a cat’s sense of smell and associated behavior can be influenced by a variety of factors, including mood, age, health, genetics, and training. By understanding these factors, cat owners can better understand their pet’s behavior and provide them with the care they need to thrive.


In conclusion, cats have a highly developed sense of smell that plays a crucial role in their survival, communication, and exploration of their environment. The anatomy of their nose, including the specialized organ known as the vomeronasal organ (VNO), allows them to detect and analyze a wide range of scents, including pheromones.

The Flehmen response, characterized by opening the mouth, curling the tongue, and pulling back the lips, is a unique behavior that helps cats to enhance their sense of smell and identify specific scents. However, there are other factors that can affect a cat’s smelling behavior, such as mood, age, health, genetics, and training.

By understanding the science behind cat-smelling behavior and the factors that influence it, cat owners can provide their pets with a safe, healthy, and stimulating environment that allows them to use their sense of smell to its fullest potential.

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