Have we seen a similar effect used in everything from The Matrix Flims to tv series such as Charmed (oooh those three young women, living in that big house all on there own...sorry I was getting carried away there) where they freeze frame a scene and you can see another actor walking behind let's say an object that was flying through the air. They must cut holes in the freeze frame video layer to allow a video layer below to show through.

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All done without the aid of a safety net...