What walks downstairs, alone or in pairs, and illustrates the finer points of earthquakes? A Slinky. In a video clip posted to the Smithsonian’s Ocean Portal Web site, educator Catherine Sutera uses the time-honored American toy to demonstrate two types of seismic waves that jostled the Washington area in August’s shake-up. The first is the P wave, a quickly moving compressional wave, which Sutera illustrates by stretching a Slinky out on a table and gentling nudging it, causing its springy spirals to move together and apart in a rippling motion. But it’s the S wave, or shear wave, that causes the real commotion. “These waves are a little bit slower than the P waves, but they tend to cause more of the damage that we associate with earthquakes because it moves in both an up-and-down and back-and-forth manner,” she explains as she whips the Slinky in both directions. So the next time the ground starts to heave like an off-center washing machine, hold on tight and think of it as a toy story.