There's lots of great trivia about Jaws, for instance Ben Gardner's head popping out of the boat was added after the film had already been finished and was being shown to preview audiences. Spielberg said he got greedy and wanted to get just one more scare out of the audience, so he filmed it in his swimming pool and added it after the fact. (This is also why the body count doesn't add up when they're talking to the mayor on the beach the next day).