Death Valley's 'sailing stones' move themselves across a dry lakebed
For decades no one ever saw the rocks of Racetrack Playa move, yet trails hundreds of metres long snaked behind them across the cracked mud. In 2014, researchers fitted stones with GPS and finally caught it happening: thin sheets of night ice, floated by a shallow winter pond, get pushed by light wind and drag the rocks along as the ice cracks apart. No animals, magnets, or hoaxers required.