Other mistake: When Dick is up in the tree fort, the aliens are looking at him through their hand binoculars, but the image is taken from the same height as Dick. However, since he is higher than they are, they would be seeing him at an angle. The view as seen would be impossible unless they were at the same height as he was.
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Suggested correction: What the camera shows is for the audience. It's not meant to be a POV shot of what the three are seeing.
