Fourteen-year-old Canyon Mansfield was out walking the family Labrador, Casey, on public land in the outskirts of Pocatello, Idaho, last month. As they roamed a hill near their home, Canyon spied a piece of metal protruding from the snowy ground that resembled the head of a garden sprinkler. When he bent down to touch it, the device exploded, jolting him off his feet and emitting a powdery substance. Some of the granules got into his eyes, which he scrubbed out with wet snow.