I have some customers that are very weird. They bring in their old cup or popcorn bag from one of their previous trips here and when no one is looking, slip it out of their coat or purse or whatever and just leave it on my counter. This sometimes happens when they are at the counter buying concessions or sometimes later during the movie. They never say anything about it and always make sure no one sees them do it. The only way I narrowed it down to them was to rewind my surveillance tape and watch it on the video monitor one day.