Revealing mistake: When Bruce and Patricia are on the crane on the roof, a wide shot of them both reveals their stunt doubles. (01:24:55)
Revealing mistake: When Carol Anne has been hypnotized by the shrink, a hand breaks through the desk and throws a coffee mug through the mirror. You can briefly see the reflection of the plexi-glass protecting the actors behind the mirror as the mirror breaks.
Revealing mistake: In the end sequence, you can see that one of the mirrors is faked, by having cables run floor to ceiling to simulate the seams. Nancy Allen bumps the cable when her mirror-double grabs her from behind and you can see it vibrate.
Revealing mistake: When Bruce and Pat get into the restaurant, chasing Carol Anne's reflection, right before Carol Anne's reflection in big mirror runs across, you can see Carol Anne crouching behind a table in reflection. Her red pajamas are very well visible.
Revealing mistake: When Scott (covered in ice) is ejected from the pool in front of Bruce, watch carefully. In the first few shots, he has some pretty convincing "ice" prosthetics attached to his body. When the camera cuts after he runs into the door, however, suddenly he's merely covered in really cheap-looking foam/slime that doesn't resemble ice in the slightest. And it's not supposed to be ectoplasm, it's supposed to be ice.
Answer: At the end of the movie, it was a different actress who played Carol Ann as the actress had already died by that point. Rumor has it that the actor who played Scott was so distraught over her death that he couldn't come back to film the scene.
lartaker1975