The horror movie "Smile" has been racking it up at the box office, which got me thinking about how many people hate smiles. I’m not talking about terrifying psychopath smiles or creepy clown smiles.

You’ve probably heard the claim that it takes more muscles to frown than to smile. It’s usually framed as a feel-good reason to turn your frown upside down – less effort, more joy. But anatomically, ...