One of the best stories in this vein was told by Reg Levy (Gaining An RAF Pilot's Brevet). Just after the war he was employed by what became Air India. He was flying DC3s with 2 pilots and an air hostess. On one trip. the hostess came into the cockpit to take away the empty coffee cups. One of the cups still had some coffee in it so she went to open one of the side vents to throw it out. The pilots shouted to stop because the other vent was already open and they explained that, if both vents were open at the same time, they would all be sucked out. On a subsequent trip with the same crew, the pilots opened both vents, turned on the AP and went to hide in the luggage compartment which was just behind the cockpit. When the hostess entered the cockpit to remove the empty coffee cups, she was met with and empty cockpit and both vents open. One can imagine her feelings.