This exercise has several interlocking levels that can expand and interact in different ways.
Have the group divide into pairs.
One person strikes a pose.
The other person then creates something around them by occupying the negative space delineated by the initial player.
The first player then drops their pose and steps back, looking at their partner once again.
They then take up a new expression of the negative space and the process begins again.
NB: You can also do this in threes by having the third player tag out one of the other two.
In this version one player continually strikes new poses, only staying still for a short length of time before moving to a new shape.
The other improviser is then continually moving around them, weaving in and out of their poses.
Remember to swap roles.
In this version, there is no lead player. Both players are striking poses, holding them for a second (or longer) before moving on. They are continually in motion.
This is a group version.
The whole class is in one circle.
One person enters the space and strikes a pose.
The next person, comes in and fills the negative space.