▲ Block a Frown, Block a Sad Thought
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From ScienceDaily, Can Blocking a Frown Keep Bad Feelings at Bay?:

The new study reported on 40 people who were treated with botulinum toxin, or Botox. Tiny applications of this powerful nerve poison were used to deactivate muscles in the forehead that cause frowning...

The results showed no change in the time needed to understand the happy sentences. But after Botox treatment, the subjects took more time to read the angry and sad sentences...

"There is a long-standing idea in psychology, called the facial feedback hypothesis," says Havas. "Essentially, it says, when you're smiling, the whole world smiles with you. It's an old song, but it's right. Actually, this study suggests the opposite: When you're not frowning, the world seems less angry and less sad."

In theoretical terms, the finding supports a psychological hypothesis called "embodied cognition," says Glenberg, now a professor of psychology at Arizona State University. "The idea of embodied cognition is that all our cognitive processes, even those that have been thought of as very abstract, are actually rooted in basic bodily processes of perception, action and emotion."

Body first, then "cognition."

UPDATE: Link to the Scientific American discussion of this study.