Okay, this one is pretty interesting.

Botox, the botulism toxin that the inject into your face to paralyze your muscles so you won't have frown line wrinkles, makes you feel happier because it makes you unable to frown and facial muscles influence brain activity.

Time Magazine Wipe Away That Frown.

If you keep reading to the bottom of the article, it gets even more odd.

"But Lewis says he favors the theory that facial muscles influence brain activity directly and points to earlier research that suggests such a neurological link. For example, studies have shown that subjects find comedy routines significantly funnier when they hold a pen between their teeth the way a dog holds a bone, a pose that stimulates the muscles used for smiling. Similarly, subjects laugh less when holding a pen between their lips, a pose that mimics frowning."

He looks pretty happy here, doesn't he?  

NY Times - Get Botox!