Continuity mistake: There is a scene where Westley is matching wits with Vizzini. In every shot of Vizzini and Buttercup, her hair changes. In one shot, half of it is over her shoulder; in the next shot it is all down her back. This happens all through the scene.
Continuity mistake: During the first scene when the grandfather is reading to the grandson, he opens the book. When he gets his glasses the book is shut and he has to open it again.
Revealing mistake: When Humperdink and the six-fingered man are on horseback near the coast, discussing strategy, you can tell that the ocean is a matte painting, as the waves and whitecaps never move.
Continuity mistake: When Buttercup and Wesley are rolling down the hill, Wesley's hair is flying all over and is quite long. When he stops, his hair is slicked back and in a pony tail.
Continuity mistake: In the scene where Fezzik, Inigo, and Westley are on the wall after Westley is tortured, Westley's hand changes position several times throughout the scene. This is odd considering he can barely move his thumb. But it changes between at least three positions several times.
Visible crew/equipment: At the end of the movie, when Fezzik is catching Buttercup jumping out the window, just as she lands in his arms, you can see the platform she jumped off at the top of the screen.
Continuity mistake: Watch the red car behind Fred Savage in the bedroom. In close shots, the car is pointing towards the camera. In wide shots it's pointing sideways.
Continuity mistake: Fezzik tries to crush Westley on a boulder. We see him doing the crushing spread-eagled, but when the angle changes to a close-up, he is holding Westley's wrists tightly under his chin.
Continuity mistake: When the Albino is cleaning Wesley's wound in the Pit of Despair, watch the rag: it goes from white to deep red and back to white between shots.
Revealing mistake: In the scene before the climb of the Cliffs of Insanity, after they get off Vizzini's ship, the end of the back of the ship suddenly jiggles back and forth like it's made of rubber.
Revealing mistake: In the duel between Inigo and Count Rugen, Inigo stabs the count in the right arm. But you can tell the sword is shorter, and it obviously wasn't stuck in the count's arm when he pulls it away.
Revealing mistake: When Fezzik is using the holocaust cloak, the long shots of him are a dummy due to the bobbing around (and the fact that they cover up the face). It's only Fezzik in the close-ups, where the hood is pulled back making his face more visible than it is in the medium shots.
Visible crew/equipment: In the duelling scene between Westley and Inigo, right after Westley has done his swinging on the bar and they go into the next shot, you can see Inigo jump up on a higher platform of rock, and then immediately after him, you can see Westley BOUNCE off the concealed trampoline onto the platform of rock.
Plot hole: In the scene where Westley is tortured to extremity, he screams, and upon hearing him scream, Inigo is instantly able to identify Westley and that he is in love with someone about to marry. You could say Fezzik told him, but how did Fezzik know? For all they knew, he was just a pirate after a prize.
Suggested correction: He doesn't instantly identify Westley; he identifies the sound of ultimate suffering. He surmises that it must be Westley because he can't think of anyone else who would have cause for ultimate suffering. By now the news would have spread that Humperdink's men apprehended a pirate claiming to be Buttercup's true love. Inigo was simply putting two and two together.
Revealing mistake: When Fezzik puts the "almost dead" Westley down on the castle wall where they look out to the gate door, the wall moves. In fact, inside the castle when Fezzik breaks down the door for Inigo, the wall moves then too.
Continuity mistake: At the beginning when Buttercup tells Westley to fill her buckets with water, her hair goes from being all over one shoulder in her closeup, to hanging down her back as she walks away. When she turns around, it's all over her shoulder again.
Continuity mistake: When Buttercup's kidnappers are arguing over whether or not they should kill her the weather goes from overcast to sunny and back again within a few seconds.
Revealing mistake: In the shot where Fezzik is putting on the harness in preparation for climbing the Cliffs of Insanity, you see the boat start to drift away. As it does, the figurehead catches on the rocks and wobbles, as if made of rubber. (00:13:25)
Continuity mistake: When Buttercup jumps down the window, she is falling in a vertical position but in the next shot, just before she falls in Fezzik's arms, she is suddenly in a horizontal position.
Continuity mistake: The iocaine-poisoned wine cups change position on the table between shots.
