Revealing mistake: Halfway through the movie, Alta is swimming in the pond, supposedly nude. However, when she climbs out, she can be seen wearing a flesh-covered swimsuit. (00:45:15)
Suggested correction: Alta never said she was naked. She didn't know what a bathing suit was and Adams assumed she was naked.
Revealing mistake: As the alien's speak to Carol, Dr. Marvin and the others inside their spaceship, they use the exact same footage again of them looking at the video screen as they leave earth even though one minute of movie time has elapsed. (00:39:25)
Revealing mistake: Toward the end of the film, when Claire Anderson enters the cave where the monster is waiting, she passes a distinctive rock formation. In a later scene, where she is going further into the cave, she again passes the same rock formation.
Revealing mistake: When the monsters are 'flying', the wires are painfully visible.