I was told about a powerful lesson in a high school class this winter. They're learning about the Salem Witch Trials, and their teacher told them they were going to play a game.

"I'm going to come around and whisper to each of you whether you're a witch or a regular person. Your goal is to build the largest group possible that does NOT have a witch in it. At the end, any group found to include a witch gets a failing grade."

The teens dove into grilling each other. One fairly large group formed, but most of the students broke into small, exclusive groups, turning away anyone they thought gave off even a hint of guilt.

"Okay," the teacher said. "You've got your groups. Time to find out which ones fail. All witches, please raise your hands."

No one raised a hand.

The kids were confused and told him he'd messed up the game.

"Did I? Was anyone in Salem an actual witch? Or did everyone just believe what they'd been told?"

And that is how you divide a community