They hid among the graves and tried to learn how to smoke, coughing a lot. Meanwhile, Albus aside spotted some large stones on the lawn and decided to get revenge: he levitated them and threw them against their backs. This time the Muggles couldn't deny that something really strange had happened. They thought about ghosts, threw away their still-lit cigarettes, and ran away as fast as they could, their shirts caught between the railings and tearing.