When Rod Steiger reluctantly took direction for a specific scene from young co-director, Stephen Carpenter, he pulled him aside and told Carpenter, "an actor is the only person whose mistakes are photographed." Carpenter went on to say in interviews that he never forgot this moment, and that it changed he and his co-director's (Jeffrey Obrow) approach to directing.
Creative horror screenwriter Joseph Stefano (Alfred Hitchcock's "Psycho") contributed to the screenplay, most notably the sequence involving the creature hiding inside of a watermelon.
Most of the interiors of the film were shot on a soundstage at David O. Selznick's famous Culver Studios, at which legendary classics such as "Gone With The Wind," "Rebecca," and "Citizen Kane" were filmed.
Susan Emshwiller's debut.
Rod Steiger performed his own stunts in a scene that involved him being doused with a 55 gallon drum of methyl cellulose "slime."