The Birds (1963) by Alfred Hitchcock.
“When I came across a DVD of The Birds, thanks to the interview with Evan Hunt (Editor’s note: the film’s screenwriter), you discover in particular that they didn’t finish shooting the planned ending, which forced Hitchcock to improvise. In fact, when the movie was released, I remember seeing photos where the heroes were walking around the city with a lot of dead birds. I tried to figure out what that was connected to and couldn’t find an answer. Now I have one: it’s from the unfinished sequence. That allowed me to understand how the movie was made and learn things about the legendary relationship between Hitchcock and Tippi Hedren during the shooting. It’s been said that he threw birds in her face for a week, out of pure sadism. That’s stupid. The real problem he must’ve had was that, once he couldn’t finish his movie they way he’d planned to, the intensity no longer existed. The last intense moment in the film was actually to be the car attacked by the birds. Since he could no longer shoot it, he had to find another one and the only one left was in the attic, which he had to make dramatic. Initially, they planned to send mechanical birds into her face, but it’s clear that it didn’t work for this sequence, the highpoint of the movie. It’s true that she was ill: at one point, she was so sick they sent her to the hospital for a week. When Rod Taylor carries her down in a sofa, it’s not her, but a mannequin. If Hitchcock had been as cynical as they say, he would have thrown in the sequence at the end of the film as is, no matter what happened to the heroine: the film was already in the can. However, what he did was a real risk. I read that Hitchcock was terrified.”