Clap out the rhythm "dada, dadada, dadadada, dada."
Split into two groups and set first group off clapping once through
Then bring in the second group after the first "dada".
While the groups are still clapping give them instructions.
i.e. cross over, walk around the room, sit down etc
You can also split the main group up into smaller groups (tribes) and set them off clapping at different times.
Stand in a circle and call each tribe into the middle to perform their clap.
The leader can act as a conductor raising of lowering the noise level and stopping or bringing different groups in.
Comment: A cracker of an exercise so long as the leader has the rhythm and timing to bring everyone in. I did this with Ali Campbell at Goldsmiths and you literally can lose sense of time and get lost in the rhythm. It is also interesting to seee how you start to relate to each other through facial expresiion and body gesture.