Common sense tells you that your actions and expressions display what's going on inside your head. But the road goes both ways: Your feelings and attitudes are also informed by what your body is doing.
If you want to like a painting more, nod your head while looking at it, as if in agreement. We implicitly associate certain actions with judgments that tend to produce them. Want to put yourself in cynic mode? Shake your head.
Do you cry because you're sad or vice versa? According to research, placing fake tears under your eyes actually increases feelings of sorrow.
If you flip someone the bird, it must be because he really pissed you off, right? Students in a lab who were asked to hold out their middle fingers while reading a story about some guy rated him as more hostile than did those who held out their index fingers.
Botox erases both wrinkles and emotions. The muscle-paralyzing drug has been shown to mute not only visible expressions of fear and anger but also the actual feelings that accompany those expressions.