Though it arguably started with Rob Reiner's 'This is Spinal Tap,' the mock-documentary comedy got a shot in the arm when 'Tap' co-star Christopher Guest used it again when he co-wrote and directed 1996's 'Waiting for Guffman.' Such led to three films that used the same style and much of the same cast . That format eventually took hold in television, and - as 'Guffman' co-writer Eugene Levy has recently said - it's so prevalent that they have no plans to make another.

Much as 'Cannibal Holocaust' prefigured 'The Blair Witch Project,' the idea of the mock-doc was nothing new when Reiner and when Guest made their films. But when it comes to television, it seems that the British version of 'The Office' was one of the first to use it successfully. And when the American version was launched, it borrowed the same style (though made much less sense).

Since then it's become standard, with shows like 'Modern Family' using the same style. This also ties into the modern "found footage" cinema movement that's becoming prevalent and cheap - with films like 'Paranormal Activity' and 'Project X.' Levy told Collider that he and Guest feel they can't do this any more, though he's open to working together again. But it's understandable that they want to stop making these things. Who wants to be called an imitator when you did it first?

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