Smiling does make you happier – under carefully controlled conditions

The idea that smiling changes the way we perceive things seemed like another casualty of social psychology's replication crisis - but something more interesting was going on

In 1988, Fritz Strack and colleagues published one of the most wonderful studies in psychology. They asked volunteers how funny they thought some cartoons were. While looking at the cartoons, some of the participants held a pen between their teeth without it touching their lips, while some others held a pen in their lips without allowing it to touch their teeth. (The participants believed they were testing out methods disabled people could use to write.)

If you try this in front of a mirror, you'll see that when you hold a pen in your lips you look vaguely as though you're frowning; when you hold it with your teeth you're grinning.