In their book How To Write Movies for
Fun and Profit, Robert Ben Garant and Thomas Lennon explain why so many Hollywood movies quote, suck donkey balls, unquote. Studio pictures notoriously cycle through writers as execs quest for the chimerical ideal balance between elements that will draw in audiences, leaving those who greenlit them unfired. As projects go through draft after draft, characters and concepts accrete to the screenplay. When a film feels like an unrealized mishmash, it’s because those elements survived to the shooting script, when though the moments they were meant to support didn’t, and are now nowhere to be seen.
The example they cite concerns the for tough-guy-meets-kids comedy, The Pacifier, which, when they first worked on it, was meant to star Jackie Chan. In their version, Jackie brings the children a live duck. Their faces light up in excitement. Jackie gets out his meat cleaver, ready to cut off the duck’s head, to prepare it for dinner. The children, being westerners, react in horror. So that's why The Pacifier prominently features a pet duck. Except that Chan dropped out of the project, which ultimately starred Vin Diesel. The meat cleaver gag got cut, because it made no sense with a non-Asian actor.
But the duck stayed in the movie.
We can extrapolate this into a saying, which we can mutter knowingly to one another as we depart in disappointment from a film that obviously lost its coherence during development hell.
“Wow, that one sure left the duck in.”