Smiles are strange things. People use them when they are happy, yes, but also when they are uncomfortable, bored, anxious, or trying to be polite. Sometimes a smile has nothing to do with joy at all.

When was the last time you laughed out loud?It is not strange if you cannot remember right away. The more tired you are, the more laughing is the first thing to be put on the back burner.Even if you ...

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, the ...