I remember playing the game of “Ha” as a young girl at my third-grade slumber party. I would lay my head of my friend’s tummy, and she would lay her head on another friend’s tummy, and so on. The first person would start the chain of laughs with a simple, “Ha!” The second person, “Ha Ha!” The third, “Ha Ha Ha,” at which point everyone would break into hysterics. About absolutely nothing. The way a person’s abdomen tightens and moves when she says “ha” makes you want to giggle.

My point: laughter is contagious. That’s why there are 5,000 laughter clubs around the world–where people laugh for no reason at all. Say what? According to Dr. Shaya of Good Samaritan Hospital, “These clubs have exercises that teach how to move your face, how to laugh more intensely to involve the shoulders, then the belly.” Laughing yoga classes are also popular today.