For any ensemble of more than one singer or instrumentalist
Play (or sing) a note in the key of C major and, at a constant metre but a different tempo to all other performers, repeat.
Play (or sing) a different note in the key of C major and alternate between your new note and the last one at the same constant tempo. Repeat.
As before, adding a further note, repeat.
Keep going, adding more and more notes from the C major scale, until all performers are cycling through the entire scale of C major at different speeds. Then, at an agreed signal, stop.