After a half-century of speculation, scientists have finally uncovered what drives the “slithering stones” in Death Valley, California, Nature reports. Hundreds of these rocks slide in stealth across the surface of the desert lakebed Racetrack Playa, leaving zigzag trails behind as the only proof of their movement. To observe the actual process, researchers deployed 15 GPS-embedded limestone rocks to the lakebed. They observed that when rain creates a shallow pond atop the playa, the water surface freezes at night, then breaks up around noon into windowpane-thin ice sheets. Helped by light breezes, the broad ice sheets could batter more than 60 rocks downstream at a time, the researchers report this week in PLOS ONE.