But the Sperwer uses a noisy engine (think lawnmower) and flies low enough to be heard. At first, the Canadian troops thought this was a disadvantage, as it let the Taliban below know they were being watched. But then the Canadians found out that Afghans had learned, when fighting the Russians during the 1980s, to fall flat on the ground when they heard aircraft overhead. From the air, the dirt colored Afghan clothes blended in with the ground, making the prone Afghans invisible.