Here's a fun fact that might ruin the first "Harry Potter" movie for you: For a considerable portion of the film, when you think you're seeing Daniel Radcliffe, Emma Watson or Rupert Grint, you're really not.
Alan Rickman, who played Severus Snape, recently revealed that often, when the back of a young character's head was shown, it wasn't really the head of the primary actor.
In the first film, if anybody ever wants to look, of course you've got the problem of kids who can only work a certain number of hours... Sometimes there were 300 children on set, and at certain points they all had to go off and do some schoolwork.
When "Harry Potter and the Sorcerer's Stone" was shot, child actors were only allowed to work four hours in a given day. Naturally, that proved to be an "organizational nightmare" for the adults working on the film.
In order to work around these restrictions, short adult actors were hired as stand-ins for the kids. Wigs were placed on their heads and the illusion was preserved.
That is, until now. Thanks for ruining this one, Rickman.