Model the exercise first,
Less pressure when everyone participates simultaneously.
Assign members of the group a partner. Have the partner groups spread out in the room so that they have space to move their arms and legs. Each partner faces each other. One person is asked to go first. They begin moving very slowly, perhaps just with a hand to begin with. While maintaining eye contact with the person across from them, their partner must begin to mirror them exactly. The goal of the activity is to mirror each other so precisely that if someone walks by they don’t know who is initiating the movement.
Suggestions for side-coaching: What parts of the body can you move? How large and how small can you make the movement? How do you gesture with your facial muscles? What movements feel habitual or comfortable, which movements feel unnatural or awkward?