Ever try to get a baby to smile? It can seem close to impossible - and then suddenly there it is: that elusive, seemingly joyous grin. Well it turns out those smiles aren't spontaneous - they're strategic.
Researchers have found that when babies smile, it's for a reason. They want whoever they're interacting with - typically a parent - to smile back. And they time it just so, a smile here and a smile there. The researchers call it sophisticated timing. The study is in the journal PLoS ONE.