Flip the sand-filled container upside down and back again to erase the previous pattern. Now, with the disk level, use the rubber hammer to knock on the flat bottom of the disk as if you were knocking on a door. You'll see the sand migrate, building up around pockets of air to form strange, shifting patterns. The vibrations you create make the sand flow like a liquid, just as the vibrations of an earthquake can make seemingly solid ground flow. The lacy patterns that appear in the sand are not well understood, and there is no easy explanation for them.
