"A few years later, a German team of psychologists conducted a simliar study. They had a group of subjects look at cartoons, either while holding a pen between their lips -- an action that made it impossible to contract either of the two major smiling muscles, the risorius and the zygomatic major -- or while holding a pen clenched between their teeth, which had the opposite effect and forced them to smile. The people with the pen between their teeth found the cartoons much funnier. These findings may be hard to believe, because we take it as a given that first we experience an emotion, and then we may -- or may not -- express that emotion on our face. We think of the face as the residue of emotion. What this research showed, though, is that the process works in the opposite direction as well. Emotion can also start on the face. The face is not a secondary billboard for our internal feelings. It is an equal partner in the emotional process."
What can we learn from this? First, if you want people to think your jokes are funny, make them hold a pen in their teeth! Second, if you're feeling down, make yourself smile anyway. A smiling face creates a happy emotion in your brain. Putting yourself into situations where you are forced to smile no matter what will actually help you to really feel happy. Don't mope around and hang out in your room by yourself. Get out there and get smiling!