Hold a stone between your fingers, lift it, and drop it into flowing water. It may not be easy to see. A ripple will form on the surface where the stone falls, and a spray will appear, but the current of the river will dampen it. That's all. Throw a stone into a lake, and its effect will not only be visible but will last much longer. The stone will disturb the still water, forming a circle where it landed. Before you know it, that circle will widen, forming circle after circle. Soon, the ripples created by the sound of the stone's impact will expand until they appear on the mirror-like surface of the water, and this circle will not stop and disappear until it reaches the shore. If you throw a stone into a river, the river will consider it just another movement of chaos in its noisy, turbulent current. Nothing unusual. Nothing uncontrollable. But if the stone falls into a lake, the lake will never be the same again.