Visible crew/equipment: During the sword fight, every time they do a large jump you can see a crash mat under the sand. (00:22:17 - 00:24:56)
Continuity mistake: When Humperdink's men are clearing out the forest, Inigo is sitting against the wall of one of the houses, drunk. The door of the hut is wide open. When he lunges at the guard who tells him to leave, the door is closed.
Revealing mistake: When Buttercup's dress catches fire in the fire swamp, Westley quickly puts it out. Light is shining through the skirt, and you can see a shadow of a hand reach out and hold the skirt so he can do so.
Continuity mistake: During the poison drinking scene there's a twig on the table that keeps changing positions in every shot.
Continuity mistake: Before the wedding, when Westley moves his head for the first time it's tilted to the right. In the close-up it's turned to the left. Then the angle changes and it's turned back to the right.
Continuity mistake: The amount of leaves around the quicksand trap increases/ decreases between shots.
Other mistake: When a disguised Westley see Vezzini holding a blindfolded Buttercup hostage, Vezzini is sitting down with a blanket, some food, two goblets and a bottle of wine. There's no way that Vezzini should have these as he wasn't carrying anything on him when he got out of the boat and Fezzik took everyone up the Cliffs of Insanity.
Continuity mistake: At the end of the film, when the grandfather is leaving the boy's room, his mustache and hair aren't grey anymore, they are both brown. His mustache is much thinner too, and his hair isn't as wavy as in the rest of the film.
Answer: Westley comes back from the sea, only to find that his one true love is engaged to another man. He feels her love for him wasn't true if she could even think of getting married again, at least so soon.
Brian Katcher