Lama Ole’s answer:
Laughter is a release of pressure. It has different meanings in different cultures. In some cultures, you show your teeth when you laugh as a sign that you’re not dangerous. Or you show your hands—that might be the first smile. This means something like, “I don’t have any weapons; I am not hiding anything,” and so on.
In the Himalayas, they laugh when someone falls. It’s not malicious joy, but rather to help the mind not hold on to what is happening. They laugh when someone trips so that the person who fell doesn’t take it too seriously. This laughter is a useful reaction.
In our culture, it’s simply liberating to laugh. When you laugh, you release energy and feel good. It’s healthy—people who laugh a lot get beautiful faces.