Corrected entry: In the film, the ghosts are only visible to the human inhabitants of the house if they are wearing special glasses. For the original film from the 1960's, special glasses were distributed because the film was made in such a way that the ghosts were only visible by wearing said glasses.
tom alma
7th Dec 2004
Correction: The original film was in 3-D, that's why the audience was given glasses.
tom alma