Other mistake: If the Maitlands cannot be seen in a reflection being ghosts, then Lydia would not have seen them in the attic window in her camera, as that uses a mirror to reflect the image through the viewfinder.
jerimiah
13th Jan 2012
Beetlejuice (1988)
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Suggested correction: However, when Lydia moves the camera away from her face to get a better look, she had both eyes open when using the camera (with her right eye looking through the viewfinder). This is a recommended technique to help get a perspective and keep one's focus on the subject. This means she could have seen the Maitlands with her left eye, the one that had a direct view of the window.
This is not how the scene plays out. She first supposedly spots them while looking through her camera, which then causes her to take a better look with the camera away from her face. She would have no reason to do that if she didn't see them in the camera, which, as we know, would not be possible given they do not cast a reflection for the mirror in the camera for Lydia to see.
Or, she just saw the curtain move and thought that was odd, then moved the camera from her face and realised there were 2 faces there. There is no indication at all that she saw them straight away.
A curtain moving from an open window is not odd. You're really reaching here, and her reaction indicates she saw far more than a curtain moving. She literally stops in her tracks and dramatically lowers the camera - the same camera that she had to her face she was looking through. Anyone who has used an SLR camera does not use two eyes open, as it is nearly impossible to focus and see things, given one eye would be zoomed in and the other would be unaided.
13th Jan 2012
Beetlejuice (1988)
Other mistake: When Adam's headless body runs into the hallway to go shut the attic door, you can see a reflection of his body when he crashes into the banister. Ghosts don't have reflections, as seen in the beginning.