The Slinky is a toy consisting of a helical spring that stretches and can bounce up and down. The toy was invented and developed by naval engineer Richard James in the early 1940s. If you hold a Slinky from the top with your hand and release the lower part, you will see something strange.
If you keep your eye on the bottom of the Slinky, you will notice that as the top of the Slinky starts to fall, the bottom doesn't drop. It will stay there, hovering quietly, until a wave, or signal, passing through the Slinky finally reaches it. Apparently, the bottom doesn't know it's supposed to fall, so it sits there, seeming to defy gravity, until the very end.
