What is happening in the scenario? A possum is playing dead.

Body System 1 and its function: Muscular System
The muscular system's main function is to allow movement

Body System 2 and its function: Nervous System
The nervous system controls your movements, thoughts, and automatic responses to the world around you.

In this scenario, how are these body systems interacting to help the organism return to normal (homeostasis)?

The nervous system sends signals throughout the body letting the possum know that are no predators near, and then the muscular systems releases its muscles to return to normal/homeostasis.