2. The Birds (1963)
The Twist: Having been attacked and trapped in a house by the world's avian population for no real reason at all, our surviving characters step outside to find that the birds have completely calmed without explanation. They drive off into the distance, pensive about the future...
Why It's Unpopular: A cop-out ending, implemented purely because Hitchcock had no other ideas how to end his picture. With no explanation as to why the birds started acting up in the first place, it's even more annoying that they suddenly decide to chill out no reason, to.
Why It Deserves More Credit: I never knew that this sudden twist of an ending was considered rather unpopular until I stumbled upon hundreds of reviews citing this part of the movie as its weakest - and going by what I've read on message boards, too, it seems like people were left feeling a little betrayed. But this is a far cleverer ending than one might realise at first, although you have to understand the core idea behind
The Birds first.
The Birds, ultimately, is about the unpredictability of nature, and how sometimes things happen and there's no way to explain them. As human beings, we constantly seek out answers and explanations for everything, and as a result things tend to happen according to the established "logic" of the universe. Which is fine, until you remember that it was us who came up with those rules in the first place. We don't actually
know what's true. So when, in Hitchcock's movie, the birds start randomly attacking, we instantly want to know why. But what if such a thing happened one day in real life? There's no reason it couldn't - we think we understand everything, after all, but we don't. Not really. So ending the movie with the birds suddenly calming down isn't a cop-out - it's a moment that sums up the entire conceit of the film: all the "rules" of the universe are still just guesses.