Give them a task. Examples include building something, cleaning something, getting across an obstacle course all together. The task must include them all getting through it together. At different stages in the task change the decision making process. For part one it can be democratic, for part two it can be authoritarian. Part three can be consensus. As they go through it write down, funny and interesting things they say. DOnt let them know that you are writing it down. After they complete the task read them the things that they said and try to assess how they worked as a team, and how they could improve.