Final answer:
The person observing should describe the change in the ball's motion, noting the combined effect of the horizontal movement with the bouncing pattern.
Step-by-step explanation:
After the first repetition of a movement pattern, such as a partner walking forward with a bouncing ball, the person running the screen should carefully observe and describe the ball's motion. This involves noting details like the trajectory, height of the bounces, and any changes in the ball's speed. In this scenario, the partner's movement adds a horizontal component to the ball's trajectory, potentially making the ball appear to have an elongated pattern of bounces compared to when it is bounced in place.