Humans are hardwired to read facial expressions because they’re integral to social communication in our species. Our brains even scan the mugs of other species to discern their mood and intent. And most people who have interacted with dogs or cats can agree they too have expressive faces, to one degree or another.
Technically, most mammalian species do. This is a unique function of the flexible skin and intricate musculature overlying their skulls. Charles Darwin was among the first to speculate about the nature of these movements with his 1872 book, The Expression of the Emotions in Man and Animals.
We tend to perceive cats as inscrutable and willfully uncommunicative. Dogs, on the other hand, are viewed as open and unabashed about telegraphing their feelings. These intuitions are so strong that they are in turn used to describe human demeanors. A person who appears mysteriously self-satisfied is said to resemble “the cat that caught the canary.” Meanwhile, someone with a sad or beseeching expression is making “puppy dog eyes.” But are these stereotypes accurate?
Research on the subject paints a complicated picture.
It’s true that cats are likely relatively hard to read. They share a much briefer evolutionary history with us compared to dogs — as much as 24,000 years shorter — so we are accordingly less proficient at decoding them. But as it turns out, they produce a suite of facial expressions just as complex as those evoked by their canine counterparts. And while we do seem to read dogs more accurately, studies have shown that we’re not nearly as adept at discerning the true meaning of their expressions as we think we are.
A deep dive into the literature tells us as much about ourselves as it does about our animal companions. In fact, some of the most detailed analyses of how animals their faces are derived from the Facial Action Coding System (FACS) developed to characterize human expressions in 1978.
Decoding Dogs’ Faces
The Dog FACS has identified over 20 descriptors of canine facial movements. These descriptions, however, are value-neutral — they don’t ascribe particular emotions to the movements. A number of studies, however, have attempted to do so.
Perhaps the most recognizable dog expression: the famous “puppy dog eyes.” In fact, dogs’ ability to furrow their brows is uniquely appealing to humans: This feature may have played an important role in the domestication process.
One hypothesis suggests that dogs’ early ancestors were wolves who became accustomed to human presence due to a dependency on their food waste. They made the jump to full partners with their hominid commensals by hacking our attraction to neotenic features — humans are innately drawn to infantile characteristics like big eyes and short snouts. The ability to wrinkle the brow — which is not found in wolves — exposes the sclera, or white of the eye, and is one of a number of factors that gives domestic dogs a more puppy-like appearance. An analysis of shelter adoptions found that dogs who make this expression are rehomed more quickly, reinforcing its adaptive benefit.
We may misread this look, though. Another study found that dogs who ate a forbidden treat made puppy dog eyes and were perceived as looking “guilty” after they were called out for the transgression. But the dogs in the study made the same “guilty” look when they were scolded and hadn’t done anything wrong. It seems that the expression was more a result of distress at their handlers’ disapproval than any true feelings of guilt.
Understanding some basic dog expressions appears to be instinctive on some level. An experiment that exposed human infants to images of dogs exhibiting both playful and aggressive expressions found that they were able to accurately match them to correlating barks.
“Adults and older kids, however, are far less accurate,” notes lead author Ross Flom, an assistant professor of psychology at Southern Utah University. “That is, older adults tend to treat all barks initially as aggressive.”
He hypothesizes that this loss of ability may be due to the cumulative time spent with dogs. “Our experience modifies in such a way that we do tend to treat each bark as aggressive.” As we grow older, we generalize barks as hostile regardless of the expression on the dog’s face. Infants, however, “use acoustic subtleties to determine or to differentiate between play and aggressive barks,” he suggests.
Strangely, another investigation found that adults who were experienced with dogs were less capable of interpreting aggressive expressions — perhaps resulting from generally positive experiences among dog lovers.
Other research casts further doubt on our innate capabilities. Younger children tend to interpret dogs’ hostile expressions as friendly: Nearly 70% of 4-year-olds viewed snarling dogs as happy, as reported in a 2011 study. This could explain dog attacks on young children who are not familiar with how to interpret their behavior.
Personality factors further complicate our interpretations of dog faces, just as they do for human faces. People who were rated higher in empathy, for example, attributed greater negativity to threatening dog faces than those who had lower empathy scores.
A handful of solid generalizations have emerged, however, allowing us to refine our intuitive perceptions. A playful attitude has been inferred from the erection of the ears, exposure of the teeth, and partial closure of the eyes. Conversely, aggression is usually signified through moving the ears forward, using direct eye contact, and opening the mouth to expose the teeth. Submission is often demonstrated by flattening the ears, lowering the head, and retracting the lips.
Generally, we appear best at interpreting our dogs’ emotional states when their whole range of behaviors, such as postural changes and vocalizations, are taken into account. So facial expressions alone don’t cut it.
Whether or not we’re interpreting them correctly, dogs appear to know that their mugs affect us. One investigation published in 2017 found that dogs were more likely to wrinkle their brows and show their tongues when humans were paying attention to them versus when they were not. Though food is perhaps an even more arousing stimulus than human attention, it did not have the same effect and suggested these expressions were not an automatic response. Instead, they were specifically directed at a human audience. This suggests that they know they’re being cute.
Reading (And Misreading) Cats
The Cat FACS has identified more descriptors than those for dogs, which is a surprising finding given the perceived inscrutability of the feline face. However, research on their actual meaning is scant in comparison to the extensive, if conflicting, literature on canine expressions.
While the canine research emphasizes social interactions, much of the feline studies have concentrated on expressions that indicate pain. Given the more limited vocal repertoire of cats and our unsophisticated understanding of their expressions, this could affect how we take care of felines: Learning to read signifiers of pain might lead to quicker medical treatment, for example.
A 2019 study published in Scientific Reports found that cats flatten their ears while experiencing pain following sterilization and raise them after the administration of pain-relieving medication. Pain was also associated with narrowing of the eyes, along with raising the upper lip and wrinkling the nose. And a Journal of Small Animal Practice investigation from 2014 found similar facial characteristics in cats suffering from pain, but concluded that most observers were unable to distinguish pain from other conditions: In that study, only 13% of participants were able to identify pain in more than 80% of cats who were suffering. Even some veterinary professionals had difficulty in accurately identifying the condition.
Unlike dogs, cats are not an inherently social species, so their facial signals may be less immediately perceptible. Indeed, they didn’t seem to matter at all in determining rates of adoption from shelters. Scientists found in 2017 that the only behavior associated with quicker adoption was pressing themselves against the front of the cage — which signified friendliness.
Other researchers have suggested that, while we do have some ability to ascertain the emotional states of our feline companions by reading their facial expressions, our accuracy is relatively low. In one study, human participants were only correct slightly over half of the time. They were far more accurate at identifying positive states than negative ones. And women were significantly better at correctly discerning how a cat was feeling by looking at its face.
“Owning a lot of cats — really loving cats — has very little effect,” says co-author Georgia Mason, an animal behaviorist at the Campbell Centre for the Study of Animal Welfare at Canada’s University of Guelph. “I thought passionate cat lovers like myself would be really good at it. But actually, we’re not.”
She notes that veterinary professionals were best at accurately identifying feline emotions. “In your life, you've probably only experienced a couple of dozen cats at close hand. If you're a professional vet, you could see dozens a year,” she observes. “Also, if you're in a veterinary practice, you’re seeing animals in much more extreme situations. Most of us don't see animals who are really in pain, or experiencing nausea, or are really terrified.”
One of the few other studies that attempted to characterize feline expressions found that frightened cats blinked, narrowed their eyes, and tended to move their heads and shift their gaze to the left. The leftward bias in fear-inducing situations may connect to the fact that the right hemisphere of the brain appears to be dominant in processing negative stimuli. Frustrated cats hissed, licked their noses, and showed their tongues. When relaxed and engaged, they moved their heads and directed their gazes to the right.
Mason suggests that further research on the subject might make cat ownership more rewarding and dispel some of the mystery associated with cats. “Some people find them too alien and too cryptic. [A greater understanding of their expressions might prove] they're not cool. They're just subtle,” she claims.
The Challenges of Interspecies Communication
Though we’ve made significant inroads in understanding the meaning of our furry comrades’ facial contortions, we have a ways to go in fully decoding them. Part of our difficulty may lie in the fact that we instinctively attempt to discern their emotions as we would those of a person: One analysis published last year in Animal Cognition found that the human gaze was drawn to the areas of a dog’s face that serve as useful indicators in human faces.
The most useful features actually only overlap to a certain degree, so we tend to miss out on the full picture. For example, ear movements are among the most significant indicators of a dog’s mood. We tend to ignore them, perhaps because humans don’t have particularly mobile ears and thus examining them would be of little help in ascertaining someone’s emotional state.
By redirecting our attention using objective characterizations like the FACS, and designing tests to empirically determine what each one means, scientists are working to incrementally close the communication gap. This could allow us to better care for our animal friends and perhaps even strengthen our interspecies relationships.