When Hulk punches Thor in The Avengers, that was one of the hardest shots to get right. HULK SMASH!
Adam Rifkin stashed this in Avengers!
Charlie Jane Anders writes:
That sequence took from the first day of the process until the very end, says White. It's one long continuous shot of the two of them working together, ending with Hulk punching Thor. For the actual punch, they put Chris Hemsworth in front of a bluescreen standing on top of a real section of a downed Leviathan that they built. And they attached Hemsworth to a cable pull that they retimed, so he could look like he was knocked sidewise. They cut a few frames out of the footage, so it looks like Hulk's punch has "instant impact," says White.
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Don't forget JimB's famous Mirror scene in Contact. It's subtle. It's one continuous scene all the way through of her as a kid running upstairs to the mirrored medicine cabinet, when you find out the whole scene had been shot through the reflection of the mirror.