8. The Visible Trap Door (The Wizard Of Oz )
It's amazing how well 1939's The Wizard Of Oz holds up to this day, with its vibrant colours, quirky characters and timeless music lending it a purely magical feel.
Still, moviemaking has advanced a great deal in the decades since, and looking back, it's easy to spot certain things that feel wrong or look out of place, like this scene where The Wicked Witch makes a dramatic exit from Munchkinland.
The character vanishing in a puff of red smoke and a stream of fire is a well-done effect, but it's hampered by two noticeable gaffes: the smoke starts billowing way before Margaret Hamilton gets into position, and the trapdoor from which it emanates is clearly visible.
But these aren't simple mistakes the filmmakers didn't notice, or couldn't correct - they knew all about it, but were forced to leave this take in the movie.
Why? Well, this was one of the only usable shots they got. In a later take, Hamilton suffered serious burns when the fire shot out of the trapdoor early, meaning she had to be treated before she could return to work.
As a result, the actress refused to do any more fire-based stunts, giving the filmmakers only one choice; to use the rehearsal take that we now see in the finished film, blatant mistakes be damned!