The Little Shop of Horrors recalled "at first they told me it was a detective movie; then, while I was flying back [to make the movie], I think they wrote a whole new movie, more in the horror genre. I think over a weekend they rewrote it." The screenplay was written under the title "The Passionate People Eater". Welles stated, "The reason that "The Little Shop of Horrors" worked is because it was a love project. It was "our" love project." The film was partially cast with stock actors that Corman had used in previous films. Writer Charles B. Griffith portrays several small roles. Griffith's
The Little Shop of Horrors with us, and the three of us worked out the rest of the story together. The first screenplay Griffith wrote was "Cardula", a Dracula-themed story involving a vampire music critic. After Corman rejected the idea, Griffith says he wrote a screenplay titled "Gluttony", in which the protagonist was "a salad chef in a restaurant who would wind up cooking customers and stuff like that, you know? We couldn't do that though because of the code at the time. So I said, "How about a man-eating plant?", and Roger said, "Okay." By that time, we were both drunk." Jackie Joseph later