Adaptation Sequence: Book —> Movie —> Stage musical —> Movie of musical —> (Extremely) short-lived Saturday morning cartoon show.
Adored by the Network: Not only did David Geffen produce both the musical and film versions of Little Shop of Horrors, he also introduced Howard Ashman and Alan Menken to his longtime friend and business colleague, Jeffrey Katzenberg, then serving as chairman of the Disney film division. As a result of this meeting, Ashman and Menken ended up having a very fruitful career for Disney, where they ended up collaborating on such Disney classics as The Little Mermaid, Aladdin, and Beauty and the Beast.
Cut Song: Most of "The Meek Shall Inherit", the "Somewhere That's Green" reprise, the end of "Mean Green Mother From Outer Space", and "Don't Feed The Plants".
Death by Cameo: In the original workprint ending, director Frank Oz is seen being eaten by the Audrey IIs invading New York.
Deleted Scene: Aside from the original ending, there's also the full "The Meek Shall Inherit" scene.
Development Gag: As he explains in a documentary about his life and music, Alan Menken's father and many of the other men in his family are dentists — something which he also began to study for but gave up in order to pursue music instead. No doubt he and Howard Ashman had fun writing the dentist's song!
Executive Meddling: The original ending was faithful to the stage musical, with the classic Greek Tragedy arc: Seymour kills his enemy, kills his father-figure, kills his love, then kills himself, and then gigantic Audrey II's go on a Attack of the 50-Foot Whatever rampage and take over the world. After preview audiences lambasted this ending for being "too disturbing", Howard Ashman wrote a happier one.
Fake Shemp: One member of the Greek Chorus wasn't available to shoot the studio-mandated happy ending, so the camera pans down before the third girl's face is seen.
Silence Is Golden: When Seymour feeds Audrey's corpse to Audrey II in the Director's Cut, the score doesn't have a chorus, unlike the play. Frank Oz stated they decided to have Seymour treat it as a ritual sacrifice.
Cut Song: Quite a few. Demos of them are available on the 2003 Broadway cast recording. The songs are...
"We'll Still Have Tomorrow": A duet between Audrey and Seymour, probably meant to take place shortly before Audrey gets eaten. Oddly, the line "we'll still have tomorrow" is sung in "Don't Feed the Plants".
"Bad": A Villain Song for Audrey II. It got reworked into "Mean Green Mother From Outer Space" in the movie, so the song would be eligible for a best original song nomination at the Oscars. (Which it received, but didn't win.) It was probably cut due to the severe Mood Whiplash that it would've caused after Audrey's death.
"A Little Dental Music": A song about Orin's practice. (Sources vary on who was supposed to sing it — some say the urchins, some say Seymour.)
"I Found a Hobby": A Villain Song for Orin, talking about how he discovered his sadism and became a dentist. This was presumably reworked into "Dentist!".
"The Worse He Treats Me": A song for Audrey, talking about her relationship with Orin. It's very "As Long as He Needs Me".