Facial expressions arise from brain networks that encode slow, context-rich meaning and fast muscle control on different time scales, keeping smiles and threats socially precise.

This is read by an automated voice. Please report any issues or inconsistencies here. Working out your face the way you work out your body makes sense. Muscles respond to movement, circulation ...

Keira Knightley and Kristen Stewart are its best ambassadors. Instead of curving upwards, their mouths curve downwards, giving them a unique charm. The inverted smile, which doesn't follow the usual ...