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What is causing hundreds of rocks to move across California's Death Valley? Is gravity responsible, or something more sinister? In New Zealand, a growing number of dogs are deteriorating in health. Scientists struggle to diagnose the symptoms, but a new clue is uncovered when lifeless marine animals begin to wash ashore. In Namibia, cheetahs are having difficulty making kills due to partial blindness. Can experts get to the root of these traumatic injuries?