Divide the group into twos and instruct them to create a short sound or rhythm that they will be asked to share with the group.
Everyone shares their sound.
Explain to the group that you as the leader will be a conductor and as you point to a pair they must make their sound/rhythm until you point to them to stop.
As conductor you can bring anyone one in you want at any Time so everybody must be watching and ready.
The conductor also shows the group other signs such as increase or decrease volume using his hands. (or lengthen or shorten sound)
The challenge is for the conductor to create as rhythmical a sound as possible.
When the conductor has had enough he can pass the baton to whoever he wants and he then joins that pair.
This can also be done with simple movement to create a dance piece
A outside pair of eyes can watch the action and look for narratives ion the movements. This can be fed back to the pairs and a scene could be devised out of this.
Shapes/movements/narratives can be paired off together to create something