If you don't know, derivatives are part of the ideas of calculus, and one way to interpret them is through slope. Now don't worry if you don't know what slope is, the derivative is just the measure of how fast a graph changes at certain points, and this just graphs that for every point. So, at the points where the graph seems flat, the animation will just trace a line that is near or at 0. if the graph is rapidly increasing, then it will trace a line that is above 0. If it is rapidly decreasing, then it will be below 0. Right now, it is really bad, I hope to add some customizable features like customizable functions, but unfortunate, no promises.