According to Jack Palance, Joan Crawford and Gloria Grahame did not get along and got into a physical altercation at one point during the filming. The fight started after Grahame sat on the edge of the set during one of Crawford's close-ups and very loudly sucked a lollipop in an attempt to anger Crawford. It worked, and Palance noted that the all male crew watched the fight for a few moments rather curiously before stepping in to break it up.
RKO and the Mutual Broadcasting System teamed up to promote the film by sponsoring a contest in which listeners were urged to write in letters explaining what their first sudden fear was and how they overcame it. The top prize was a trip to Hollywood.
This film's initial television presentation took place in New York City 7 February 1958 on The Late Show on WCBS (Channel 2), followed by San Francisco Friday 7 March 1958 on the Major Movie on KRON (Channel 4), and by Los Angeles Saturday 12 April 1958 on the Fabulous 52 on KNXT (Channel 2).
The trivia item below may give away important plot points.
Most of the film makes excellent use of actual San Francisco and Bay Area locations. However, the climactic ending scenes, where Lester chases Myra through the streets, were filmed in the Bunker Hill neighborhood of Los Angeles, starting at the point after Lester leaves Irene's Russian Hill apartment and gets in his car.