Why Are Emotions Contagious?

Have you ever been in a group of people who got the giggles? One person starts laughing about something no one else seems to have noticed, and soon everyone is cracking up. Or maybe you’ve had your mellow completely harshed by the Eeyore in your group. It’s as if our emotions harmonize, converging on a pitch, low or high. It’s the kind of thing most of us have noticed, at least occasionally.