Dario Marianelli was considered as a possible composer for this film.

Evanna Lynch beat 15000 girls and 29 finalists for the role of Luna. When it came to viewing the finalists, she was the ninth person in the audition videos and one of the producers, David Barron stopped viewing after her saying, "She is Luna." Unknown to them, Lynch actually wrote a letter directly to J.K. Rowling.

The Department of Mysteries set marks the first time that a totally computer-generated set was used throughout the movie. Building the set practically is too expensive since an estimation of 15000 crystal balls are needed and it will take a lot of time to clean and setup again if a retake is required.

Imelda Staunton was the producer?s only choice for the role of Umbridge. She and costume designer Jany Temime came up with the idea of making her dress more padded and more saturated as the film progresses. The novel describes her being physically chubby and like a toad.

The Room of Requirement was described as a room with no beginning nor end. To achieve the sense of infinity, the effects crew spent 5 months designing the room by having rotatable mirrors installed that would minimize camera and crew reflection as well as to avoid the Hall of Mirrors effect (a common term in CG). Also, another problem on the set is that the lighting underneath the grille was quite bright to generate reflection; so the floor had to be in black, cast members had to have black velvet covering their shoe soles while the crew has to wear blue surgical shoes to prevent treading dust onto the floor set.

The film's fake working title was called Tip-Top.

Professor Umbridge, though she teaches in a classroom that has appeared in films two through four, inhabits an office vastly different from those of her predecessors. The set was redressed with "fluffy, pink filigree," including a carpet that cost ?50,000 to make, and a number of plates upon which moving kittens were animated in post-production. A 24-hour photo shoot was held to photograph and film the kittens for use on these plates. Even the elegant quill which Umbridge gives Harry to write lines using his own blood was designed by the set designers.

Helen McCrory was originally cast as Bellatrix Lestrange, but due to pregnancy she had to be replaced by Helena Bonham Carter. McCrory was later cast as Narcissa Malfoy, who is Bellatrix's sister, in Harry Potter and the Half-Blood Prince (2009).

The radish earrings worn by Luna Lovegood were actually made by Evanna Lynch (the actress portraying her).

Mira Nair and Jean-Pierre Jeunet were approached to direct the film. Both declined.

The character of Grawp was done by using a recent breakthrough in film technology, developed by Image Metrics, which allows a computer to map an actor's performance onto any character virtual or human, living or dead. The result is said to be far superior to standard hand-drawn computer graphics which are very costly and time-consuming.

Release prints were delivered to theaters with the fake title 'The Raven'.

During the breakfast scene in the Great Hall, a box of cereal can be seen with the name Cheeri-Owls with a color scheme similar to that of a Cheerios box.

According to the original script, the character of Kreacher was not intended to be in this film at all. But after J.K Rowling read the script, she more or less insisted on him needing to be there to avoid some serious problems with future installments of the series. So, even if Kreacher still has no noticeable impact on the plot or story as it's presented in the film, a couple of scenes with him were added at the last minute based on this request.

Daniel Radcliffe came up with the idea that, as a gesture of respect to a teacher that Harry most certainly looked up to, he would wear a certain type of clothes that resemble the outfit worn by Prof. Lupin in his lessons from Harry Potter and the Prisoner of Azkaban (2004), during his teachings. The director liked the suggestion, so that became t

Continuity

(at around 30 mins) When Harry, Hermione, Ron and Neville are in the carriage with Luna her hair is curly, yet in the next scene (what would be shortly after) her hair is completely straight.

(at around 34 mins) When Harry is asleep during his first night at Hogwarts, he is wearing a striped, light blue T-shirt. But when he has a vision of Voldemort and sits up in bed, his shirt is now solid dark blue with buttons.

In the veil room, when the Death Eaters have all but Harry at wand-point, Bellatrix is shown first holding Hermione hostage. Immediately in the next shot she is being held by a male Death Eater, and Bellatrix is shown later to be holding Neville at Wand-Point.

(at around 4 mins) When Harry is fighting off the Dementors, he produces a patronus and his wand is pointing at the Dementor that attacked him. When the scene cuts to Dudley on the ground, Harry's wand is at his side. When it cuts back to Harry, his wand is pointing at the dementor again.

(at around 38 mins) When Harry reports to Dolores Umbridge's office for discipline, she straightens a single crookedly placed pen on her desk. Later in the scene, the pens are no longer all in alignment.



Factual errors

(at around 1h 13 mins) Phineas Black's name is misspelled "Phineus" on the tapestry at Grimmauld Place.

Near the beginning, when Harry, Dudley and Mrs Figg are walking home shortly after the dementor attack, it is night-time. The ministry's letter states that the attack took place at 6.23pm. However, in August, in Surrey, England, sunset is not until 8pm.



Incorrectly regarded as goofs

(at around 1h 21 mins) In Harry Potter and the Goblet of Fire (2005), when Harry is looking in the Pensieve, Igor Karkaroff accuses Barty Crouch Jr. of torturing Frank and Alice Longbottom. In The Order of The Phoenix, after a DA meeting, Neville tells Harry it was Bellatrix Lestrange. Both statements are in fact true, as according to the books Frank and Alice Longbottom were tortured by a group of Death Eaters, which included both Barty Crouch Jr. and Bellatrix Lestrange.

Only a few characters can see the Thestrals, but anyone can ride them after being helped to mount them by people that can see them, just as a blind person can ride an ordinary horse. This is how so many students can ride the Thestrals to London.

(at around 37 mins) Umbridge punishes Harry for an outburst where he claims that Voldemort killed Cedric Diggory in the previous film, Harry Potter and the Goblet of Fire (2005). Cedric Diggory was really killed by Peter Pettigrew (Wormtail), but only after a direct order from Lord Voldemort. Voldemort can be said to be analogous to Adolf Hitler (and others alike), who did not personally carry out his killings.

(at around 21 mins) During Harry's trial, Fudge pronounces the name of the court as the "Wizenagamot"; the real name being the "Wizengamot". This could be intentional, to further underline Fudge's incompetence as Minister.

(at around 18 mins) When Harry and Mr. Weasley are descending into the Ministry, using the visitors' entrance, only the inside of the phone box in the street moves. When the scene cuts to the interior of the Ministry, they're in a complete phone box. However, if you look closely you can see that there is in fact a frame moving inside the original phone box, clearly it is a double. Otherwise, guests would have been in danger of falling off.



Revealing mistakes

(at around 1h) During the first "D.A." training/meeting, harness and wires are visible as characters are thrown back after being struck by a spell.

(at around 1h) When Nigel blasts Harry backwards, the retraction line pulling him is briefly visible, as is his safety harness.

During the hearing, when Mrs. Figg has just described the dementors, and Fudge starts talking again, there is a close-up of Harry, with no scar.

In the Department of Mysteries, Neville Longbottom (Matthew Lewis) looks up to see the prophecy orb with Harry Potter's name on it; however, when Harry (Daniel Radcliffe)-who is several inches shorter than Neville-takes the prophecy from the shelf, the orb is at his eye level.

In multiple shots throughout the movie you can clearly see that Harry's glasses have no lenses in them.



Anachronisms

Petunia is seen watching the weather on a flat screen TV. The film, like the book, is set in 1995 and flat screen TVs did not appear until the mid to late 2000s.

(at around 31 minutes) in the Gryfindor common room there is music playing in the background. The song is "Boys Will Be Boys" by The Ordinary Boys, which was not released until 2005 but this film is set in 1995 a full 10 years before the song's debut.

(at around 18 mins) When Harry is being escorted by Arthur Weasley to his hearing at the Ministry of Magic, the two find themselves in a tube station which contains barriers that one may gain access through by use of an Oyster Card. J.K. Rowling has gone on record to state that Harry was born on July 31st, 1980. This would mean that the fifth installment in the Harry Potter series would take place in 1996, for Harry's fifth year in Hogwarts would see him being 16 years old. As this is the case, Oyster Cards would not exist at this time due to the fact that they were first invented in 2003. This mistake is under the pretense that the Harry Potter universes' time line was the same as the real world's, with the fictitious addition of the magical world.

At 5 minutes and 13 seconds the Dursley car number plate can be seen. The film takes place in the year 1995, however the number plate style is that of a post 2001 UK number plate, specifically the year 2006.



Audio/visual unsynchronized

(at around 1h 45 mins) When Lucius has Harry and company at wand point in the Department of Mysteries, Bellatrix Lestrange walks out from behind him. In the audio she is laughing maniacally and talking to Harry, but when you look at her, her mouth is barely moving. She mouths "He knows how to play" a full second after it is heard, and her mouth moves at a much slower pace. She also has a deadpan expression on her face, not the maniacal face you would expect her to have while laughing like that.

(at around 2h 5 mins) Near the end, when Harry and Luna are having a chat, when Luna says '...if not always in the way we expect', she is not moving her lips at all.



Crew or equipment visible

When Harry is first looking at the veil in the Department of Mysteries, bars of blueish light connected to either side of the arch are visible.



Errors in geography

(at around 1h 45 mins) When Harry and his friends fly on the Thestrals to London, they are coming from Hogwarts, which according to the novels is somewhere in Scotland. So if they are flying from the North of the UK towards Westminster in London, where the Ministry of Magic is located, there is no reason why they would fly over the Canary Wharf district, which is 5 miles east of Westminster, especially if they are in a hurry to save Sirius Black.



Plot holes

It is known from the previous movie that memories can be extracted and viewed through magic, yet when Harry needs to prove his claims on his Wizengamot hearing, nobody thinks of doing this to Harry's memories of that night, or Dudley's, who, although a Muggle, knows about the magical world. While this was probably deliberate from Fudge, as part of his determination to convict Harry, it makes no sense from Dumbledore, who defends Harry on the trial.

(at around 43 mins) When Harry sees the thestrals dragging the carriages, the others cannot see them. Luna then claims that he can only see them because he has seen death (Cedric, as he could not see them in previous years). Although JK Rowling said that he wouldn't have recalled his mother's death clearly enough because of him being just a baby at the time. he did watch Quirell die before him in Harry Potter and the The Sorcerer's Stone. So he should have been able to see Thestrals since, at the earliest, his second year at Hogwarts.

As Harry trains Dumbledore's Army in the room of requirement, they practise extensively with Expelliarmus spells. This should have resulted in mass chaotic shifts of wand allegiances.

(at around 1h 45 mins) Bellatrix Lestrange has been imprisoned for 14 years, well outside any contact with society, so how does she know (or recognise) Neville Longbottom the second she sees him? He was barely one year old 14 years ago.

During the battle between Voldemort and Dumbledore, their wants engage in priori incantatem. It is established that this is a phenomenon caused by "sibling wands". As Voldemort's wand and Harry's wand are siblings, this would not work between Voldemort's wand and Dumbledore's wand (the Elder Wand).



Character error

Neville says that he never performed an Expelliarmus spell before, but in one of the previous Dark Arts trainings (within the sequence where Filch, Draco Malfoy & co. try to enter the Room of Requirement) he clearly performs one.

(at around 1h 26 mins) When Umbridge is holding detention, one of the Weasley twins dips his quill into the ink well, even though no ink is needed for these quills.

(at around 9 mins) Mad-Eye Moody tells Kingsley to take point as they escort Harry to headquarters, but throughout the flight Moody is in the lead. During the flight over the Thames River - just before the ferryboat - Kingsley can be seen to Harry's left. Moody should have told Kingsley to guard their flank.

There is no reason for Mrs. Figg to say last year when she says "after You-Know-Who killed that poor Diggory boy last year...", it happened just a couple of weeks ago.

Despite Harry's previous experience with Dementors, he never thinks to offer Dudley some chocolate at home, especially seeing how angry Aunt Marge and Uncle Vernon are.