“Shopping carts are one of the simplest forms of herd robot. A single store can support a huge corral of shopping carts in a vibrant, active community. The shopping carts from a large store can make many, many migrations through the store each day, or rest outside within bounds of the parking lot, socializing and nesting with other carts. As new carts approach mating age, they will spend more of their days roaming the perimeter of the parking lot, away from the other carts, far from safety. Sometimes they are maimed or destroyed by delivery trucks.”