What: At a key moment in the 2004 film Harry Potter and the Prisoner of Azkaban, Harry and his friend Hermione Granger have used a time-turner to travel back three hours to free the hippogriff Buckbeak and rescue Harry’s uncle Sirius. In the middle of a life-threatening series of events, Hermione sees a previous version of herself from three hours earlier. Suddenly distracted (and at the precise moment the picture at right shows the past-Ron Weasley, Hermione, and Harry turning at the future-Hermione’s outburst), she delivers the time-stopping question, “Is that really what my hair looks like from the back?”

Why: Bizarrely, the greatest line in all of the Harry Potter stories was not written by J.K. Rowling. After two pulseless films, director Christopher Columbus stepped aside to produce the third film in the franchise. He turned to, of all people, Alfonso Cuarón, the director of the erotic Mexican film Y tu mamá también. Cuarón spun a tale far more compelling than any other offering in the series. He was aided by a trio of young stars—Daniel Radcliffe as Harry, Rupert Grint as Ron, and Emma Watson as Hermione—coming into their own as actors. Here, they had a tricky scene to pull off. In the book, Rowling could explain the characters’ time-tripping activities. But the movie audience needed a visual reason for the two sets of teens to interact. Cuarón and screenwriter Steve Kloves gave Watson the line to end all teenage-girl lines. Hermione’s shocked realization was everything you would expect from an insecure 13-year-old. It made her a real girl.

Impact: It also made Watson a real actress. While critics found Radcliffe a bit wooden, Watson gained nothing but praise. A rather un-bookworm-like flattening of Draco Malfoy didn’t hurt matters. Meanwhile, despite being the boldest of the films, Prisoner of Azkaban had a comparative struggle at the box office, grossing the least of the series. For Goblet of Fire, Cuarón was replaced by noted British director (hey, there’s a novel idea) Mike Newell, and the series continued crushing the competition all the way through today’s release of Harry Potter and the Half-Blood Prince.

Personal Connection: Most people reading this know that I know J.K. Rowling, at least superficially. We met when I was the creative director on the Harry Potter Trading Card Game and associated projects, and found a certain ability to talk on each other’s level. In the brief time I interacted with her, I found Rowling to be clever, engaging, and fiercely possessive of her characters. And yet she allowed us a great deal of freedom to invent and shape her world, in small part because I told her we wouldn’t screw it up. This Hermione line was the first time I thought the film series felt that freedom as well.

Other Contenders: James Dean’s Jimbo Stark is torn apart in Rebel Without a Cause; The Runaways’ Cherie Currie salutes her parents with a “Cherry Bomb”; the dying Johnny tells Ponyboy to “stay gold” in S.E. Hinton’s novel and later film The Outsiders; Peter Parker struggles through webslinging puberty in the cafeteria scene in the film Spider-Man; the detainees let loose in The Breakfast Club, including Ally Sheedy’s Allison revealing what happens when you grow up; after years of holding it in, Filter’s Richard Patrick asks his dad what he thinks about him at 3:15 into “Take a Picture”.