The actors who played the main trio in 'Harry Potter' were given homework by the film's director. It turned out just as you might expect from their characters!
The third 'Harry Potter' film, 'The Prisoner of Azkaban' was directed by Alfonso Cuarn.
Cuarn wasn't the first choice to direct the film, and was initially nervous about accepting as he had not read any of the books or seen the films.
After reading the series, he changed his mind and signed on to direct, as he had immediately connected to the story.
The director's first exercise with the actors was to give them a homework assignment.
The main trio Radcliffe (Harry), Grint (Ron) and Watson (Hermione) were tasked with writing an autobiographical essay about their character, written in the first person, spanning birth to the discovery of the magical world, and including the character's emotional experience.
Radcliffe handed in a simple, one page essay, perhaps something Harry would do.
The other two were even more strikingly similar to their characters, however. Watson submitted a detailed, 16-page essay much as Hermione would have, while Grint didn't write his!
When asked why, Grint said "I'm Ron; Ron wouldn't do it." This satisfied Cuarn who said "Okay, you do understand your character."