Organise the group into a circle., ensuring enough space between each other (stretched arm length). Stand in the middle of the circle. The aim of the game is for all participants to exactly copy your movements – all except two of them. Instead of these two movements, they must make another movement which has been set by you prior to the game e.g. when put your hands on the back of the head, the players must squat, or when the when you bend forward, the players must clap their hands etc. Anyone that makes a mistake is out of the game.
You can adapt this to suit the sport or subject that you are teaching.