Hogwarts and Beyond: 17 More Hidden Gems From the Harry Potter Books and Movies – Part 4

In Harry Potter and the Order of Phoenix, when they discover the Room of Requirement, Ron asks if it could become a bathroom if the user really needed it. This is a reference to the novel 'Harry Potter and the Goblet of Fire'. In it, the Room of Requirement is mentioned for the first time, having become a lavatory for Dumbledore.

Padfoot, Sirius Black's canine form, animagus, was played by a Scottish Deerhound named Cleod.

J.K. Rowling had been a schoolteacher before writing the Potter books, and Order of the Phoenix features some references to the British educational system. In the late 1980s and early 1990s, students at age 16 were given Ordinary Level (O-Level) exams in all their major subjects, for which they can receive their General Certificate of Education. This corresponds to the Ordinary Wizarding Level (O.W.L.) exams given at Hogwarts. Students who planned to go on to university stayed on two more years to take their Advanced (A-Level) Exams, which roughly correspond to N.E.W.T. (Nastily Exhausting Wizarding Test) Exams.

Over 30,000 individually placed tiles were used to create the Ministry of Magic sets in Harry Potter and the Order of the Phoenix. As real ceramic tiles would have been far too expensive to produce, they were instead made out of heavily-painted cardboard.

Author J.K. Rowling revealed that the character of Dolores Umbridge in the Harry Potter series was based on a real person whom she "disliked intensely on sight", and whom "returned [her] antipathy with interest", even though she honestly could not explain why they hated each other so much.

When Dumbledore's Army first meets at the Hog's Head Inn in Order of the Phoenix, there is a bartender accompanied by a goat, played by Jim McManus, and credited as "Barman." This character is later identified as Aberforth Dumbledore, the Professor's younger brother. This character returns in Harry Potter and the Deathly Hallows: Part 2 (2011), and is played by Ciarán Hinds.

In the books, the entire plot of Goblet of Fire is foreshadowed when Harry and Ron are doing their divination homework. While they're doing their divination homework, Harry and Ron mention: a "danger of burns" (1st task), losing a "treasured possession" (2nd Task), being "stabbed in the back by someone you thought was a friend" (either Barty Crouch Jr. or Ron being an ass after Harry was chosen as champion) and coming "off worse in a fight" (the fact Voldemort comes back and can now touch Harry).