Mirror movements are characterized by involuntary movements on one side of the body mirroring voluntary movements on the other. For example, if someone wanted to pick up a pencil with their left hand, then their right hand would also reach out for the same pencil. This mostly affects the top half of the body but can also affect the bottom half. Walking may become more difficult, as one leg will move at the same time as the other. Playing a musical instrument such as the piano may become very difficult, as the process involves doing different things with each hand.