JOHANNESBURG – At first, the drone took some explaining. Anxious villagers buzzed with rumors of a new blood-sucking thing that would fly above their homes. The truth was more practical: A United Nations project would explore whether a small unmanned aerial vehicle, or UAV, could deliver HIV test samples more efficiently than land transport in rural Malawi. Once understanding dawned and work began, young students and their teachers would spill out of the nearby school, cheering, each time they heard the drone approaching. "It was very exciting," UNICEF official Judith Sherman said.