The giant rodents were created with diminutive actors inside rat suits. On the day Westley was supposed to battle the giant rat, the "rat actor" was pulled over for speeding and subsequently arrested, and actually had to be bailed out of jail by the filmmakers so the scene could be filmed.
During the filming of some scenes, the weather became markedly cold for Robin Wright. André the Giant helped her by placing one of his hands over her head; his hands were so large that one would entirely cover the top of her head, keeping her warm.
When Count Rugen hits Westley over the head, Cary Elwes told Christopher Guest to go ahead and hit him for real. Guest hit him hard enough to shut down production for a day while Elwes went to the hospital.
While rehearsing for the film, André the Giant's thick accent prevented many of his lines from being understood. To remedy this, actor Mandy Patinkin slapped André in the face to get him to concentrate harder.
When asked what his favorite thing about making this film was, André the Giant replied, without skipping a beat, "Nobody looks at me." He felt treated as an equal, without people staring at him because of his grand height.
Writer William Goldman was on set during one of the flame burst scenes in the forest when Robin Wright's dress caught fire. Although Goldman knew this was intentional, he was so caught up in the moment that he shouted, "Her dress is on fire!", thus ruining the take.
Most of the movie was filmed on location in England. The castle used for the film was Haddon Hall, a fortified country house (not a castle as such) that dates to before 1087 (when it was listed in the Domesday Book). The tapestries in Haddon Hall interiors are original, dating to the late medieval and renaissance periods.
Mandy Patinkin claims that the only injury he sustained during the entire filming of this movie was a bruised rib due to stifling his laughter in his scenes with Billy Crystal. His attempt at holding back his laughter is obvious from his facial expression during his line, "This is noble sir."
In a 2012 interview in New York Magazine, Mandy Patinkin said that his most famous line from The Princess Bride (1987) ("Hello. My name is Inigo Montoya. You killed my father. Prepare to die.") gets quoted back to him by at least two or three strangers every day of his life. Patinkin told the interviewer that he loves hearing the line and he also loves the general fact that he got to be in the movie.
According to author William Goldman, when he was first trying to get the movie made in the 1970s, a then-unknown Arnold Schwarzenegger wanted to play Fezzik, and he was strongly being considered because Goldman could never get his first choice, André the Giant, to read for the role. By the time the movie was made about 12 years later, Arnold was such a big star they could not afford him, Andre was cast after all and the two big men had gone on to become friends.
Cary Elwes and Mandy Patinkin performed all of their own sword-fighting after many hours of training. According to Rob Reiner, the only stunt performed by Patinkin's stunt double was one flip during the 'Chatty Duelists' scene.
Despite his character Fezzik's almost-superhuman strength, André the Giant's back problems at the time prevented him from actually lifting anything heavy. Robin Wright had to be attached to wires in the scene where Buttercup jumps from the castle window into Fezzik's arms because he couldn't support her himself.
There were no "shrieking eels" in the original novel. Instead, once Buttercup jumps overboard to escape her captors, Vizzini warns her of sharks in the water, and fills a cup with his own blood and throws it in the water to attract them.
While shooting scenes on top of a high grassy slope, Cary Elwes broke his toe. André the Giant couldn't walk up that hill, which was a huge slab, so he drove a rented, small four-wheeler and threw Elwes the keys to try it. Elwes went over a rock, which got caught between his toes and the pedal, crushing his toe. He couldn't delay the shoot and thus shot his scene. In the film, you can see him limping when he's running into the swamp. Costume designer Phyllis Dalton made a special shoe for him.
There really was a "Dread Pirate Roberts" (Bartholomew Roberts, also known as Black Bart) who operated in the Caribbean in the early 18th century. He is reckoned by many to have been the most successful pirate of all time.
The fencing masters that Inigo and Westley talk about studying are all real fencing masters from the 14th to 16th centuries (although the styles of fighting they are using have little to do with what those masters actually taught).
Mel Smith (The Albino) has confessed to never having watched his performance in this film due to the painful experience involved in filming the role. His character required him to wear coloured contact lenses and, unknown to Smith and the costume department at the time, he was actually allergic to the lens solution used. This meant that Smith was in constant pain and discomfort throughout filming; hence, he is reluctant to relive the memory.
Vizzini's advice on not getting involved in a land war in Asia is derived from principles stated by Field Marshal Bernard L. Montgomery (Viscount Alamein) in a speech in the House of Lords on 30 May 1962: "Rule 1, on page 1 of the book of war is: 'Do not march on Moscow.' ... Rule 2 is: 'Do not go fighting with your land armies in China.'"
The video baseball game the Grandson in playing during the first scene is "Hardball" produced by Accolade, Inc., in 1985. It was widely available in the mid-1980s for the Commodore 64 computer system. It was a one or two-player game. The sound was not from the actual game, but later added.
While never stated in the movie, according to the screenplay the grandson and grandfather live in the Chicago suburb of Evanston, Illinois. This explains the Walter Payton Chicago Bears #34 jersey worn by the grandson, the Chicago Cubs pennant and William Perry poster on the wall and the Chicago White Sox cap hanging in the room.
Robin Wright and Cary Elwes were smitten with each other during filming, naturally helping their chemistry in the movie. Cary said that he "couldn't concentrate on much of anything after that first encounter with Robin."
Director Rob Reiner considered a lot of different actors to play Fezzik before André The Giant finally got the part. One of the actors considered to play the part was Richard Kiel, who is most famous for portraying Jaws in two James Bond movies.
The trivia items below may give away important plot points.
Mandy Patinkin revealed that acting out Inigo's quest to avenge his father's murder brought back memories of losing his own father to cancer in 1972. He said that when filming the scene when Inigo kills "The Six-Fingered Man" he felt like he had just "killed" the cancer that killed his father.
Count Rugen wounds Inigo five times before and during the period of the film: the two cheek scars he inflicted on Inigo when he was a child, sword thrusts to one forearm and the opposite shoulder, and the knife wound in the stomach. When Inigo finally gets the upper hand in their duel, he returns exactly those wounds and no more: first the forearm and shoulder, then the cheek slashes, and then finally he kills Rugen with a thrust to the stomach.
Buttercup is continually referred to throughout the film (and in the film's title itself) as "The Princess," even though she is not yet married to Humperdinck. However, the grandfather states that Buttercup was born on a small farm, and Humperdinck states in his speech to the people that she was once a commoner. The reason for the discrepancy is that in the novel, the law of the land did indeed allow Humperdinck to choose his bride, but that bride was required to be a princess. Humperdinck overcame the obstacle by making Buttercup princess of a nonexistent country, making her eligible to marry him.
Count Rugen's death in the original novel was more graphic. After telling the "son of a bitch" he wants his father back, Inigo proceeds to cut Rugen's heart out, even describing what he's doing to Rugen, claiming that the count had figuratively done the same to him when he murdered his father years before (Inigo even tells Fezzik earlier on, "That is the sound of ultimate suffering. My heart made that sound when Rugen slaughtered my father. The Man in Black makes it now.") However, before Inigo finishes cutting out the Count's heart, Rugen dies of fright.