I saw this on late night TV as a teenager, and remember certain cast members. That was the only way I was able to find this film in the database. I cross referenced Mary Wickes with the butterfly collector on a Gilligan's Island episode. His name escaped me then, but it is John McGiver. Recently I bought a copy of the original book, and it was well written. The basic plot is the same, but Castle's comedic treatment did take away from the scarier aspects of the story. Incidentally Nathaniel Benchley, the author of the book was the father of Jaws author Peter Benchley. Humorist Robert Benchley was Nathaniel's own father. I keep requesting this to play on Turner Classic Movies to play it, but I doubt it is classic enough. Maybe if they do a b-series of William Castle gimmick films it will fit the format. Paramount handles distribution of it. Maybe it will come out on DVD some day...
***Update*** I bought the eastern European import DVD from a Florida company, and watched it today. It is as amusing as I remember -- very much in the "spirit" of the madcap sixties decade in which it was made.
As is often the case, it pales in comparison to the original media. But that argument is so old its cliché. I'd like to see the book made into a true horror movie, but that's for a different forum than this. If this movie ever is released on DVD in the USA, I expect it to go straight to the $5.50 discount bin. But I do bet it gets snatched up by people like us. Us being the people that look up this movie on IMDb.