Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. 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.…