Final answer:
Newton's Third Law dictates that for the gravitational force pulling Rey downward, there is an equal and opposite reaction force, which is the upward force exerted by the couch.
Step-by-step explanation:
In the given scenario where Rey is sitting on a couch, according to Newton's Law of Action-Reaction (Newton's Third Law of Motion), for every action force there is an equal and opposite reaction force. As gravity exerts a downward force on Rey, the reaction force is the upward force of the couch that Rey is sitting on. This opposing force is also known as the normal force, which prevents Rey from falling through the couch.