If no one sees you eat it, it has no calories. If you drink a diet soda with a candy bar, they cancel each other out. When eating with someone else, calories don't count if you both eat the same amount.
Foods used for medicinal purposes have no calories.
Movie-related foods are much lower in calories simply because they are a part of the entertainment experience and not part of one's personal fuel. This includes Milk Duds, popcorn with butter, Junior Mints, Snickers, and Gummi Bears. Cookie pieces contain no calories because the process of breakage causes calorie leakage. If you eat the food off someone else's plate, it doesn't count. If you eat standing up the calories all go to your feet and get walked off.