El estrangulador invisible

Being a film of mostly former A-list guest stars like Sue Lyon and Elke Sommer, character-actor Frank Ashmore, who plays the central killer/antagonist, is far down in the credits. In fact, his name shows up in the middle of a "stack" of names. This could be because he was one of the few unknown actors in this film, or the fact he's invisible a lot of the time.

Barrett tells the crew "Don't forget that telephone" and the following shot shows them with said telephone already in hand, dusting brush poised, so they were already not forgetting it before he told them not to.

The DVD version released as "Astral Factor" is a rather different movie from the DVD released as "The Invisible Strangler." The killer is not only seen throughout in "Astral," but talks frequently (as opposed to never in "Invisible Strangler," where he is also invisible after the first scene up until the end) Most of the scenes he is in, including the opening where he first becomes invisible, is completely reshot with a different cast, features different music (as does much else of the movie), has different action, and often strikes a different tone. "Astral Factor" also fills in many missing plot points from "Invisible Strangler" with the inclusion of material edited out from the other version, which are usually easy to spot by grease pencil marks on what is obviously a work print. The running time is about ten minutes longer for "Astral," despite the fact that the opening scene, in its completely different version, runs about that much shorter than the one in "Invisible."

Featured in Horror Hotel: The Astral Factor (2018)