Continuity mistake: When Westley and Inigo are duelling, Westley flings his sword so that it sticks into the ground and then athletically flips from a bar to where the sword is and nonchalantly reaches down and back and takes it out of the ground. But if you watch, he lands too far away from the sword to do this.
Trivia: When Count Rugen knocks Westley out to put him in the Pit of Despair, Cary Elwes wanted the scene done properly, so he told Chris Guest to hit him for real with the sword butt. Guest did, and accidentally hit him hard enough that production had to be shut down for a day while Elwes was taken to the hospital.
Vizzini: Inconceivable! Give her to me. Catch up with us quickly!
Fezzik: What do I do?
Vizzini: Finish him, finish him - your way.
Fezzik: Oh, good. My way. Thank you Vizzini. Which way's my way?
Vizzini: Pick up one of those rocks, get behind the boulder. In a few minutes, the man in black will come running around the bend. The minute his head is in view, HIT IT WITH THE ROCK!
Fezzik: My way is not very sportsmanlike.
Inigo Montoya: That Vizzini, he can fuss.
Fezzik: ...fuss...fuss... I think he likes to scream at us.
Inigo Montoya: Probably he means no harm.
Fezzik: He's really very short on charm.
Inigo Montoya: Oh, you've a great gift for rhyme.
Fezzik: Yes, yes, some of the time.
Vizzini: Enough of that.
Inigo Montoya: Fezzik, are there rocks ahead?
Fezzik: If there are, we'll all be dead.
Vizzini: No more rhymes now, I mean it.
Fezzik: Anybody want a peanut?