* Emma Thompson accepted the role of Professor Trelawney to impress her four-year-old daughter, Gaia. Tilda Swinton was originally offered the role but declined.

* Other directors reportedly considered for this installment of the Harry Potter series included Callie Khouri and Kenneth Branagh. Branagh had played a major role in the preceding film, Chamber of Secrets.

* Dudley Dursley has no lines. He only laughs at the TV and gives two gasps of surprise.

* During the credits on the Marauder's Map watch for: Footprints that turn into paw prints. Footprints that chase other footprints. Cat prints that chase owl prints. Extra-large footprints by Robbie Coltrane's credit. Footprints that take special interest in the closing credits' creator. Two pairs of footprints in a scandalous configuration in a corner turret. Footprints that scurry away when the page covering them is lifted. Footprints that get stuck in an alcove. Footprints that walk into a room labeled "The Grindylow Lagoon", then sink. Hogsmeade landmarks, including the Book of Monster's Repair Shop and The Stink Bomb Shop. Toward the end, footprints can be seen playing hopscotch. By the listing for the song "La cumparsita" (The song played in the TV Show that Dudley Dursley is watching after Aunt Marge has flown out the window) a set of footprints can be seen tapping one of their feet. Also look for what look dance class footprints by the composer credit, and two sets of footprints walking backwards from the visual effects supervisor's credit.

* The effects team spent six months creating the dementors. Originally, Alfonso Cuarón wasn't thrilled with the idea of using CGI and wanted to use more traditional techniques such as puppetry. The filmmakers tried a basic technique with a dementor puppet floating in the breeze but weren't satisfied with the way it looked. Puppeteer Basil Twist showed them a technique that involved putting the puppet in water and shooting it in slow motion with the film reversed. The filmmakers liked the way it looked but realized that this would be an impossible task, so in the end they decided to use CGI to create the dementors.

* Honeydukes "is floor-to-ceiling psychedelia" and includes Mexican skulls made of sugar. The cast was told that the Honeydukes candy was lacquer-coated, when in fact it wasn't, to prevent candy from disappearing between takes.

* Illusionist Paul Kieve served as a consultant. He taught magic to several members of the cast including Daniel Radcliffe and Emma Watson (Harry and Hermione) and worked extensively to create physical magical effects. He is the first illusionist to have worked on any of the series of films. He is also to make a cameo appearance in the film in a scene in the Three Broomsticks pub.

* Filming was halted following the vandalization of the train used as the Hogwarts Express.

* The set for Honeydukes was previously used as Olivander's Wand Shop in Harry Potter and the Sorcerer's Stone (2001), and Flourish and Blotts in Harry Potter and the Chamber of Secrets (2002).

* David Thewlis was originally considered to play Professor Quirrell in Harry Potter and the Sorcerer's Stone (2001).

* The film was offered to director Guillermo del Toro but he opted to do Hellboy (2004) instead.

* Marc Forster was offered the job of directing this film but declined and did Finding Neverland (2004) instead.

* The tattoos on Sirius Black's body and hands are borrowed from Russian prison gangs. They are markings which identify the person as a man to be feared and respected.

* Gary Oldman says he accepted the role of Sirius Black because he "needed the work". He hadn't acted for over a year. His last film was Sin (2003/I), which was filmed in 2002.

* Alfonso Cuarón coached Daniel Radcliffe in one scene where the latter had to act awed: "Pretend you're seeing Cameron Diaz in a G-string". It worked.

* Cameo: [Ian Brown] the singer (formerly of the Stone Roses) appears briefly in the bar at the start of the movie reading "A Brief History of Time". He was originally cast as the pub landlord, but the role was cut right down due to timing issues.

* Executive producer Chris Columbus (who directed the first two films) offered the role of director to Alfonso Cuarón after watching Cuarón's A Little Princess (1995).

* Alfonso Cuarón had never read the Harry Potter books or seen the first two movies when he was offered the job of director.

* When we see the Marauder's Map for the first time, the name 'Newt Scamander' can be seen. In the Harry Potter universe, he wrote the book "Fantastic Beasts and Where To Find Them", but isn't a teacher at Hogwarts.

* Because he would be overseeing this film's post-production work, director Alfonso Cuarón declined the offer to direct Harry Potter and the Goblet of Fire (2005). 'Mike Newell (I)' was then chosen by Warner Brothers.

* The German subsidary of Warner Bros. tried to cut down the film (as they did with Harry Potter and the Chamber of Secrets (2002)) to secure a more commercial "Not under 6" rating. They submitted several versions but all were rejected by the German ratings board FSK for this rating. In the end the uncut version was released with a "Not under 12" rating.

* Broke UK box office records when it grossed £5.3 million in its opening day of release on 31 May 2004, making it the biggest opening day and single day of all time.

* Warner Brothers supplied ushers at cinemas with night vision goggles to prevent illegal recording and pirating of the film.

* The film contains several commemorations to director Alfonso Cuarón and his Mexican heritage. On the fountain in the courtyard in front of the clock tower, there are several statues of eagles eating snakes. This exact image appears on the Mexican flag. Also, among the many candies offered at Honeydukes are skulls made of sugar, which are a popular treat in Mexico on "El Dia de los Muertos," or the Day of the Dead. And, after Dumbledore says his final lines outside the infirmary, he goes down the stairs humming "La Raspa", the Mexican Hat Dance.

* The rating in the Netherlands for this film is "not under 9". This rating was created especially for the film, since it was judged to be too scary for 6 year olds and the next rating, "not under 12", would exclude too much of the target audience.

* Aware of his fondness for music, Gary Oldman presented Daniel Radcliffe with a bass guitar as a gift when they met.

* In the scene where Harry is given the Marauder's Map by the Weasley twins, the name "Moony" is misspelled as "Mooney". While not really a mistake, there is still an interesting connection. The film's visual effects supervisor is named Karl Mooney. The spelling was changed deliberately for the in-joke.

* When Harry, Hermione and Ron are returning to the school from Hagrid's hut after witnessing Buckbeak's execution, Hermione hugs Ron and Harry hugs Hermione, a reference to Alfonso Cuarón's movie Y tu mamá también (2001).

* The set for the sequence where Professor Lupin teaches Harry to defend against the dementors previously served as Dumbledore's office in Harry Potter and the Chamber of Secrets (2002).

* When the Boggart takes the form of a giant snake, the "snake pit" theme from Raiders of the Lost Ark (1981) is worked into the soundtrack by John Williams who also did the music for that film.

* Director Cameo: [Alfonso Cuarón] the man seated holding two lit candles when Harry enters Madame Rosmerta's Tavern.

* Sir Cadogan, played by Paul Whitehouse, was cut almost completely out of the film. You do still see Sir Cadogan jump into the shot of Ron, Harry and Hermione right after Ginny tells them the Fat Lady is gone. He appears in a picture behind them.

* A fire near the Glenfinnan viaduct in Scotland delayed filming of the Hogwarts Express scenes for a day.

* Two Knight Buses were built: one for exterior shots and one for interior shots. The exterior of the bus was created by taking an ordinary double-decker London bus, adding a level, and painting it purple.

* Ian McKellen turned down the role of Dumbledore. Having appeared as Gandalf in The Lord of the Rings, he said, "I had enough trouble living up to one legend. Two would be too much to hope for."

* Ron's dream about spiders making him tap-dance is a two-in-one reference of the next book. In 'Goblet of Fire' there is an unforgivable curse where you can control what someone does, taught by Professor Moody. He makes a spider tap-dance on the desk.

* Prior to its release, material related to the film was labeled with the code title "Radiator Blues".

* Professor Dumbledore seemingly stalls the executioner by saying that he needs to sign the execution order, and that he has "a very long name". In Harry Potter and the Order of the Phoenix (2007), his full name is revealed to be Albus Percival Wulfric Brian Dumbledore.

* During the scene where we first meet Buckbeak the Hippogriff, just after Ron pushes Harry forward there is a shot of the animal pooping. The CGI team believes this might be the first example of a CGI animal doing this, but the BBC miniseries "Walking with Dinosaurs" (1999) had done it first.

* Alfonso Cuarón had an idea for there to be tiny people inhabiting Hogwarts, and jumping on piano keys in one scene. J.K. Rowling firmly vetoed it, saying tiny people were completely foreign to the world of her books.

* When Chris Columbus was still slated to direct, Robson Green was considered for the role of Sirius Black.

* Shot entirely on wide-angle lenses. The length of the lenses ranged between 14-24mm and never beyond that. Alfonso Cuarón insisted on the wide-angles because he wanted to let the audience see the foreground and the background.

* During the filming of the sleeping bag scene, director Alfonso Cuarón and Alan Rickman played a practical joke on Daniel Radcliffe by hiding a remote-control-operated Whoopee Cushion in his sleeping bag. According to Cuarón, Daniel tried really hard to stay in character while everyone else was laughing.

* Two Persian red cats were used for the role of Crookshanks: Crackerjack and Pumpkin.

* Much of the filming was done in Scotland, so the filmmakers wanted to be sure that a Highland Cow, a breed of cattle native to Scotland, appeared in the film. The large, hairy animal with big horns can be seen in front of a shop in Hogsmeade when Ron and Hermione go and look for Harry after he leaves the pub.

* Among the difficulties associated with filming in Scotland was the amount of rain that fell during the shoot. During the breaks in filming, helicopters delivered large bags of gravel to the set in order to prevent it from washing out. Many of the filmmakers were concerned as to how this would affect the look of the film, although director Alfonso Cuarón and cinematographer Michael Seresin insisted that it was the best look that they could have come up with.

* A clause in Alfonso Cuarón's contract forbade the director from cursing in front of the kids on set.

* In order to acquaint himself with his three lead actors, director Alfonso Cuarón had each of them write an essay about their characters, from a first-person point of view. Emma Watson, in true Hermione fashion, went a little overboard and wrote a 16-page essay. Daniel Radcliffe wrote a simple one-page summary, and Rupert Grint never even turned his in.

* The lyrics to the song the choir sings in the Great Hall, "Double, Double; Toil and Trouble..." and the tag line of the movie "Something wicked this way comes" are made up of lines from William Shakespeare's "Macbeth" (Act 4, Scene 1). The words are recited by the three witches, referred to throughout the play as the Weird Sisters. In Harry Potter and the Goblet of Fire, a band called 'The Weird Sisters' come to play at Hogwarts.

* The tune played on the gramophone during the Boggart scene is NOT Louis Prima's "Sing, Sing, Sing". The actual song, "Swing, Swing, Swing" written by John Williams, is from the film 1941 (1979) and is also featured in "The X Files: Triangle (#6.3)" (1998) during the sixth season.

* Cinematographer Emmanuel Lubezki (frequent collaborator of director Alfonso Cuarón) was supposed to be working on this film, but due to scheduling conflicts he was replaced by Michael Seresin.

* Director Alfonso Cuarón's wife, Annalisa Bugliani and daughter, Tess Bu Cuarón appear in the film as the mother and baby in the portrait next to the Fat Lady's portrait.

* The symbols under Sirius Black's picture on the Wanted Poster translate as "more or less human."

* An additional set was built for the candy shop: the cellar. Not used in the film, it was included in a special feature on the DVD release that allowed viewers to explore the shop.

* Subplot involving the Sneakoscope concept from the novel, as well as an attempted attack on Ron in his sleep at Hogwart's by Sirius Black, were filmed (and can be partially found as additional scenes on some DVD versions) but ultimately scrapped from the finished version. Oddly enough, a small bit from the latter, Harry's lines about missing a chance to get to Sirius, was still featured prominently in most promotional trailers. (Source: 2-Disc DVD extras & trailers).

* After the death of Richard Harris, many actors were considered for the vacant role of Albus Dumbledore. Christopher Lee was in the frame for a while, and there was a rumor (reported in many newspapers) that Ian McKellen was also considered. The Harris family wanted Peter O'Toole for the role but O'Toole declined. Richard Attenborough also lobbied for the role but was ultimately turned down.

• Continuity: When Harry, Ron, and Hermione are talking to Hagrid about Buckbeak's execution we see Harry get up and walk away from the rock he is sitting on. But in the next shot, Harry is sitting back down on the rock.
  
  
• Continuity: During his conversation with Fudge, Harry's arm switches position on the back of the chair.
  
  
• Continuity: When Harry is interrogated by Professor Snape about the Marauder's Map in the darkly-lit hallway, the drawstrings on Harry's sweatshirt change position. In one shot, they fall parallel, but in the next shot, they criss-cross. Also, when Lupin is talking to Harry in his classroom minutes later, the drawstrings switch from being cris-crossed to falling parallel between shots.
  
  
• Continuity: Ron's pimples move about his face from one shot to the next.
  
  
• Continuity: The spot on Harry's shirt in the finale moves from a large, dark spot over his breastbone to a less distinct spot over his right ribcage.
  
  
• Crew or equipment visible: When Harry is bowing to Buckbeak in the pumpkin patch near the end of the movie, you can see the bulge of his microphone battery pack, which is under the back of his sweatshirt.
  
  
• Crew or equipment visible: You can sometimes see lighting devices reflected in the characters' glasses. As Harry is telling Hagrid "It'll be fine" as they are hurrying out the door, you can see lighting equipment reflected in Harry's glasses. Also, in Trelawney's first class, you can see similar lighting equipment reflected in her glasses.
  
  
• Continuity: In Hagrid's hut the first time, Hermione opens the back door to leave and sticks her head out before Hagrid opens the front door to let in Dumbledore and Fudge. When time is turned, you can clearly see that Hagrid opens the front door before Hermione opens the back door.
  
  
• Continuity: When they're in the Shrieking Shack, Ron is pointing as he says "He's an animagus!" however, his hand then goes from pointing to holding Scabbers between shots.
  
  
• Continuity: On the train, the bottle of water is on the left-hand side of the tray. However, when the bottle of water starts freezing, it is in the center of the tray. After the Dementor attack, it is on the left of the tray again.
  
  
• Revealing mistakes: When the Whomping Willow hits Harry and Hermione, they land on the grass hard. However, as Hermione gets up, she pushes down on the grass they are on, and you can tell that it is separate from the rest of the grass around them. They obviously landed on a softened mat rather than the regular ground.
  
  
• Continuity: In the hut, when the rock comes flying in the window, it breaks the urn into three large pieces. When we see it broken again later, it breaks into several small pieces.
  
  
• Crew or equipment visible: When Lupin is talking to Harry about Harry's parents a piece of lighting equipment is reflected in Harry's glasses.
  
  
• Crew or equipment visible: When Harry blows up his aunt, you can see the cables that she is attached to.
  
  
• Continuity: When the DADA class lines up to each have a go at the Ridikkulus Charm, Seamus is clearly behind Ron in the queue, followed by Harry. Once Ron ends his turn, Parvati is then next (not Seamus), followed by Harry.
  
  
• Continuity: The mud on Hermione's trousers changes throughout the time-turner scene.
  
  
• Continuity: During the night, when Harry goes looking for the Peter Pettigrew he saw on the Marauder's Map, when Snape catches Harry, Harry puts the map in his front pocket, the shape of the map being in his pocket changes from shot to shot.
  
  
• Continuity: When in Hagrid's hut, the rock gets thrown at a jar in the house. One time when Dumbledore and Fudge are coming, the next when Harry and Hermione go back in time. The jar breaks differently in each scene, even though technically it's the same shot.
  
  
• Crew or equipment visible: As Harry and the others run up the stairs to the Fat Lady picture for the first time, you can see the markers on the floor where characters have to stop for focus/lighting reasons. They're white crosses on the floor with gaffer tape.
  
  
• Incorrectly regarded as goofs: Both times that the Marauder's Map is activated visibly, Moony is spelled 'Mooney' when the text appears on the parchment. The spelling in the book has no e. However, this is a deliberate in-joke, made in tribute to the film's visual effects supervisor, Karl Mooney.
  
  
• Continuity: The length of the chain used for Hermione's Time Turner varies throughout the film - sometimes it's quite long and other times it's barely longer than a normal necklace.
  
  
• Miscellaneous: In the closing credits, "Book of Monsters Repair Shop" is misspelled "Book of Monster's."
  
  
• Continuity: During the first Divination lesson, Professor Trelawney picks up Neville's cup from the table in front of Dean Thomas, comments on it, puts it back on its saucer and moves on. Immediately afterwards Neville grabs the same cup now standing directly on the tablecloth.
  
  
• Continuity: When Snape is filling in for Lupin in Defense Against the Dark Arts, Hermione's Time Turner changes from hanging over her robe, to under, then over again between shots.
  
  
• Continuity: On the Knight Bus, as Stan Shunpike holds the newspaper in his hands the position of the hat on his head changes between shots.
  
  
• Revealing mistakes: In the later part of the movie, when a cloud moves to reveal the full moon, Harry and Hermione's faces light up as though a light shines directly in front of them. The moon however, is to their right.
  
  
• Continuity: In the CoMC class, when Harry is approaching Buckbeak, Ron is behind him. Sometimes he has his "Monster Book of Monsters" under his left arm, and sometimes the book is missing.
  
  
• Continuity: At Hagrid's hut, after Harry, Ron, and Hermione sneak out the back and are hiding behind the pumpkins, when Hermione turns and looks over her shoulder at the sound of the breaking branch, as they go to leave, she turns back around to face the cabin before heading off to her left. When 'time turned Harry and Hermione' are watching themselves, when Hermione turns and looks behind her, she continues turning to her right to leave, never facing the cabin.
  
  
• Continuity: Lupin changes position between shots shortly before Harry takes his turn to fight the boggart.
  
  
• Continuity: When Harry and Hermione are hiding from the werewolf, and they back away from a tree, Hermione is 2-3 steps behind Harry and closest to the werewolf. In the next shot, she is in front of Harry as he puts his arm around her to protect her.
  
  
• Continuity: In the finale, when Harry passes out (the first time), he stays conscious long enough to see the light of the patronus fade, therefore, he sees himself. When time-turned, however, he passes out before the light of the patronus fades.
  
  
• Crew or equipment visible: (In the Widescreen Edition only) In the Leaky Cauldron, when Mr. Weasley pulls Harry aside to talk to him about Sirius Black, the number 301 briefly flashes in the bottom left side of the screen below the "Have you seen this wizard?" poster.
  
  
• Revealing mistakes: During the boggart scene when they show the front view of Parvati you can see that Daniel Radcliffe's stand-in is standing in line and not him.
  
  
• Continuity: Harry's grip on Buckbeak when they fly early in the movie changes between shots when they pull in for a close-up.
  
  
• Crew or equipment visible: When Hermione jumps over the branch of the Whomping Willow, you can see the cables pulling her up.
  
  
• Revealing mistakes: When Hermione angrily knocks over the crystal ball during the last Divination scene, a red and black tube can be seen jutting out of its side.
  
  
• Continuity: When Harry is bowing to the hippogriff, his tie is done up wrong - the thin part is much longer than the front part. But when he is riding the hippogriff his tie is done up properly.
  
  
• Continuity: When Neville is being scared by Trelawney, his hands are alternately above table level and below table level.
  
  
• Continuity: When Harry is under the invisibility cloak and throwing snowballs at Malfoy and his cronies, there is a point at which he pulls down the pants of Crabbe and kicks him. In the next shot, Crabbe who was previously on the ground is now standing up, perfectly fine, while the other one is on the ground in the position of the first.
  
  
• Continuity: While Harry (hiding under the Invisibility Cloak) is attacking Malfoy, Crabbe and the third thug in Hogsmeade, he leaves no footprints behind in the snow. However, in all other Hogsmeade scenes, Harry leaves footprints in the snow.
  
  
• Continuity: When Harry is in Lupin's office in the second to last scene, the Marauder's Map is on the desk in one shot and isn't in the next, however, there is no indication that Harry has picked up the map.
  
  
• Revealing mistakes: During the first shot inside the Leaky Cauldron, you see a waiter make a bottle disappear. If you look closely, you can tell that not only was the bottle tipped on its side to appear as though it had disappeared, but it's still visible under the cloth used to wipe down the table.
  
  
• Continuity: When the line forms to battle the Boggart, there is a boy between Ron and the girl that fights the snake. After Ron's turn, he is still there for a brief shot, but she then goes next and he is no longer seen.
  
  
• Revealing mistakes: When Neville tries to open his Monster Book of Monsters and gets attacked by it, you can see that a large amount of the paper supposedly shooting out of the book is coming from nowhere near the book.
  
  
• Errors made by characters (possibly deliberate errors by the filmmakers): The first time we see Buckbeak, Harry's scar is on one side of his forehead. The camera shot then cuts to Buckbeak, and back to Harry, and we see his scar is on the other side of his forehead.
  
  
• Continuity: Hermione's hair length grows back and forth all along the movie, often between chronologically adjacent scenes, in a manner not consistent enough to suppose that she gets haircuts.
  
  
• Revealing mistakes: In many scenes either Harry Potter's scar is on the left, then the right and sometimes there is no scar.
  
  
• Crew or equipment visible: At the beginning of the film, when Aunt Marge enters the Dursley's, she is closely followed by a camera under a umbrella, just before it cuts to a shot from behind Aunt Marge.
  
  
• Plot holes: When Harry is under his invisibility cloak on the way to Hogsmeade, Fred and George grab him with their arms wrapped around Harry's. They can't do that as the cloak would either be in the way or would be knocked off a bit. The cloak doesn't make him non-solid so it makes no sense.
  
  
• Errors made by characters (possibly deliberate errors by the filmmakers): On the Knight Bus, when the shrunken head is counting while the old woman crossing the street it says ten, nine, eight, seven, six, five, four, three, three and a half, two... when is supposed to say three and a half, three, two... clearly this was deliberate joke, matching the counting with the old woman's slow pace.
  
  
• Revealing mistakes: After Harry comes out of the pub when he finds out that Sirius is his god-father, just before Hermione takes the cloak off, you can see some snow on the green sheet used to make the cloak.
  
  
• Continuity: The windows in Hagrid's house are closed when Harry, Ron and Hermione visit him but they are open when the stones are thrown through it.
  
  
• Miscellaneous: During one scene when Harry is walking through Hogsmeade in his Invisibility Cloak, his footprints show up directly in between the very solid legs of someone walking.
  
  
• Revealing mistakes: When Malfoy is hit by the first snowball, he flinches before the snowball actually hits him, which is supposed to be done by surprise.
  
  
• Continuity: The position of Uncle Vernon's hand on the stair banister whilst confronting Harry after Aunt Marge blew away.
  
  
• Continuity: In the scene where Hermione punches Malfoy in the face, you see her point her wand to his neck with her right hand. When she turns around you can still see the wand in her right hand. When she actually punches him, she uses her right hand, but there is no wand in it.