Four people create a pattern often seen in square dances. Have each play with improvisations that exhibit rotational symetry. Two fold rotational symmetry and two reflection planes. When the groups have learned how to differentiate between these symmetries, have them work more free form, inventing a series of shapes which they are able to cycle through smoothly without giving verbal cues. It is important to say, expecially for non-dancers, that movement need not be dance class vocabulary.
Ordinary movements work well here when performed with energy and clarity.