In a circle everyone closes their eyes.
One person is secretly picked to be the leader. (Maybe tap someone on their shoulder while everyones eyes are closed).
Open eyes and everyone must workout who is the leader.
Instruct leader not to obviously do anything
Show it in your eyes, shoulders, posture, breath.
Ask the group who they think the leader is.
Once the leader is established ask the group to say how could they tell/not tell who was the leader.
You can have more than one leader
You can make everyone the leader
Don't make anyone the leader