A false cast that consists of a forward and a back cast causes the fly to travel on a loop path that finishes when the next forward cast starts. The path of the rod tip detemines what sort of loop is created. The energy that is needed to make this happen is transferred from the rod to the line. The stops cause the rod to unload resulting in a wave that starts running through the entire line. A caster tries to dampen the rod tip to get rid of the shock wave to straighten the line but he observes the fly line from the side. So if the rod is dampened well and the line speed is high the waves might disappear from his point of view. But they do not really. You will always see these waves traveling through the entire line when you look right from the front or the back into the loop.
