When you want to use a smile GIF, at least one in 10 are of dogs that grin or appear to smile, with their mouths wide open. But do dogs really smile? And if they do, does that mean they're happy? Maybe, but a lot depends on context, say canine experts.
The dogs in those GIFs really are doing something with their faces. The lips are pulled back. The mouth is open. But what we see, i.e. a smile, and what the dog feels don't always line up.
Dog faces are wired for expression
Anne Burrows, an anatomist at Duquesne University who studies the comparative anatomy of facial expression in dogs, has studied enough dog and wolf faces to know that the muscles underneath work very differently. Dog facial muscles are mostly fast-twitch — meaning they contract quickly and can produce the fleeting movements we associate with spontaneous expression.
"The faster your muscles are, the more genuine the facial expression is," Burrows tells Popular Science. "Dogs are our best friends. They tell the truth. We can count on them to let us know how they're feeling."
Wolves have more slow-twitch face muscles, Burrows says. Those muscles are better suited to holding the lips in a steady funnel to howl than to flicker through expressions. Dogs aren't just friendlier wolves. Their faces evolved differently.
Burrows has noted in a study that dogs' shift to fast-twitch facial muscles wasn't accidental. Dogs whose faces moved quickly were easier to read, and over tens of thousands of years, those were the dogs that humans kept around. Wolves signal to wolves. Dogs signal to us.
But a dog "smile" isn't always a smile
That doesn't mean every dog's grin-shaped expression means what we think. Karen Jesch, a PhD student at Boston College's Canine Cognition Center, points out that human smiling is a strange behavior to begin with, and not always a happy one.
"If you look at our closest relative, the chimpanzee, when they pull their cheeks back and part their lips and expose their teeth, that's usually a fear grimace. It signals that they're anxious or displaying submission," Jesch says.
Dogs do something similar. A dog might pull its lips back into something that looks like a smile, but that expression might actually mean the dog is uneasy, not happy. A relaxed mouth hanging loosely open is more likely to mean a dog is at ease. But humans tend to read both as smiling.
We're worse at reading dog faces than we think
Research has shown that humans are not as good at reading dog facial expressions as they assume, Jesch says. Part of that is anthropomorphism, the urge to map our own feelings onto animals. Sometimes, she says, that does the dog a disservice when they aren't actually having a good time.
The classic example is the "guilty look." A dog cowers when its owner discovers a chewed shoe, and we read shame on its face. But experiments suggest the look isn't really about guilt. It's what Jesch calls an "appeasement signal" triggered by the owner's body language — the dog's way of trying to defuse the situation before it gets worse.
"They're more likely just doing an appeasement signal to say, please don't be mad at me," Jesch says.
Context matters. A "smiling" dog curled up on the couch next to you is probably content, Burrows says. The same expression in a loud, chaotic environment, paired with a tucked tail, might mean the dog wants to leave.
Dogs don't communicate just using their faces, however. Burrows points out that dogs rely heavily on their ears, too. Relaxed ears usually mean a dog is approachable; ears pinned flat against the head usually signal fear or stress.
So is a smiling dog actually happy?
Sometimes, yes. A relaxed open mouth, soft eyes, a loose body, and a wagging tail in a calm setting probably mean a dog is enjoying itself. The same teeth-baring grin in a tense moment, with a stiff body and pinned ears, is something different, and worth paying attention to.
The good news, Jesch says, is that humans can get better at this. "If everybody who loves dogs were to spend a little bit of time learning how to interpret their signals, I think we could help them live much happier lives."
So, the next time you fire off the smiling-dog GIF, know that might not be an expression of joy. Certainly, the dog in the image is doing something with its face — what it means depends on what else is happening around it.