In order to acquaint himself with his three lead actors and actress, 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 sixteen-page essay. Daniel Radcliffe, like Harry, wrote a simple one-page summary, and Rupert Grint, like Ron, never even turned his in.
Sir 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." He also stated it would have been inappropriate to take Richard Harris' role, as the late actor had called McKellen a "dreadful" actor.
(At around one hour and twenty-three minutes) Originally, the script called for Hermione to slap Malfoy as opposed to punching him. During rehearsal for the scene, Tom Felton told Emma Watson to slap him, however, he had intended for her to not actually hit him, and thus was taken by surprise when Emma smacked him across the face as hard as she could. Emma said she felt terrible about it afterwards, and didn't know what she was thinking.
Director Alfonso Cuarón had never read the Harry Potter novels, nor seen the first two movies, when he was offered the job of director. It was Guillermo del Toro who convinced him, saying: "Don't be stupid; read them immediately."
Director Alfonso Cuarón had the idea to have Harry, Ron, and Hermione wear everyday clothes more often than their Hogwarts uniforms in order to show more of the characters' personalities. He also gave the rest of the Hogwarts students permission to wear their uniforms any way they wanted to in order to bring a greater sense of realism to the wizards' school, hence some of the students wear the uniforms very neatly, while others have the shirts and ties hanging out.
Annalisa Bugliani, Bu Cuaron: (At around twenty-seven minutes) Alfonso Cuarón's wife and daughter are the mother and baby in the portrait next to the Fat Lady.
Ian Brown: (At around twelve minutes) the singer (formerly of The Stone Roses) appears briefly in the bar at the start of the movie, reading "A Brief History of Time" by Stephen Hawking. He was originally cast as the pub landlord, but the role was cut down due to time constraints.
Alfonso Cuarón: [Mexico] References to Cuarón's Mexican nationality abound. On the fountain in the courtyard, in front of the clock tower, there are several statues of eagles eating snakes, as on the National Seal of Mexico. Also, among the many sweets offered at Honeydukes are skulls made of sugar, known as Calaveras, 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.