Which are best movies theories that make sense?

A fantastic twist finishing, secret meaning or a great disclose can make a film more amusing to watch and re-watch, but every so often, it's the fans of the specific movie who come up with a good theory which makes the actual movie look even more excellent than it could on its original. Not each fanmade theory is as enthused or crafty as the finest of them, but they often make viewing a classic film twofold as much enjoyable. Guys, which are the most wonderful movies theories you came up with or heard from other fans?