- Dario Marianelli was considered as a possible composer for this film.
- Evanna Lynch beat over 15,000 girls for the role of Luna Lovegood.
- The carpet in Professor Umbridge's office cost 50,000 to make.
- Daniel Radcliffe, Rupert Grint, Emma Watson and more of the cast and crew were spotted filming on the Westminster Underground Tube station in London. This is thought to be the filming of the St. Mungo's scene.
- 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 the 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 the bases for his look during those scenes.
- In Harry Potter and the Chamber of Secrets (2002), when Ron is rescuing Harry from the Dursley's, Ron tells Harry that they we're "rescuing you of course". In this film, Moody says the same thing when he rescues Harry.
- Broke the Wednesday opening day record previously held by Spider-Man 2 (2004) with a 44.2 million dollar domestic gross.
- Was released in 4,181 US theaters. A record for a Warner Bros. release.
- Had the biggest IMAX opening ever, pulling in $1.9 million.
- Harry's, Ron's and Hermione's signatures for the Dumbledore's Army roster are the same signatures seen in the books.
- The most expensive set was the 200 foot-long hallway in the Ministry of Magic.
- All of the action scenes were shot using hand held cameras.
- In the scene where Harry, Ron, and Hermione are discussing Harry's kiss with Cho, the three begin to crack up near the end of the scene. This was all real laughter from the three actors. The director thought it was good for the scene and kept rolling.
- Had the biggest first-day gross of a "Harry Potter" movie.
- The Hall of Prophecies is entirely computer generated, including all the shelves & every single orb on them.
- Padfoot, Sirius Black's canine alter-ego, was played by a Scottish Deerhound named Cleod.
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