To those on the inside, of course, nothing is funnier than an inside joke. But the real significance of inside jokes is what they mean for those who aren't on the inside. Laughing at a joke creates an incentive to join the joke-teller. But not laughing?not getting the joke?creates an even greater incentive. We all want to know what we're missing, and this is one of the ways that revolutions spread from the small groups that spawn them.