In the Goat Island story, what organism was the predator and wich one was the prey?

First of all the reason the graph would be a curve is because, as the time increases the position changes, at first the ball is at a certain point then it starts rolling off a cliff so its moving foward and then the ball starts falling, (If too confusing here is a image http://www.mazzworld.net/U11Image1.gif)