When Joel Thornton at the University of Washington in Seattle and his colleagues looked at records of lightning strikes between 2005 and 2016 from the World Wide Lightning Location Network, they noticed there were significantly more strikes in certain regions of the east Indian Ocean and the South China Sea, compared with the surrounding areas. Unusually, they occurred along two straight lines in the open ocean, which coincided with two of the busiest shipping lanes in the world. Along these paths there were twice as many lightning strikes as in nearby areas.