There are lots of variations on the idea of changing
between moving and stillness. Some ideas ...

Individuals - freeze at ding
Pairs - one moving, one still - switch
at ding
Group - half moving, movers gives impulse to stationary who
move off (can give impulse to a different person)
Group - when one freezes
everyone freezes.
Group - when one freezes others join in a sculpture till
all still
Group - when one freezes others join them in same pose until the
initiator starts moving again, this is nice in big groups because there can be
several still groupings around the room.