you know, how did I often do at that time? first I stood inside the room. opened the door a little bit. put a pail with some water in it on the top of the door. then waited for someone. once someone passed my home, I shouted," hey, come here, I have something for you to eat." then this guy ran towards me happily. when he pushed the door, the pail fell down at once. and the water poured onto his body.