At the first squelch, I knew the film would be ruined. Out of the corner of my eye, I had seen her unwrap the gum, pop the wad in her mouth and masticate it experimentally. But worse was to come. The stranger sitting next to me, at the screening of the meticulously restored print of the 1970s kung-fu classic, The 36th Chamber of Shaolin, was a talker. Simon Busch talks cinema etiquette.