P.L. Travers, the author of the Mary Poppins books, criticized the script of the movie the way some people pick at a hangnail. She had tons of objections: she didn't want it to have songs, she didn't like the animated sequence, and she even objected to using the color red in the movie. (Source)

You can blame the voice coach. The cockney accent Dick Van Dyke used to play Bert was widely criticized for being inaccurate. (It's still considered one of the more inaccurate English accents in movies—along with Keanu Reeves' accent in Bram Stoker's Dracula). (Source)

If things had work out differently, Walt Disney's most iconic image wouldn't have been two circular mouse ears, but two long bunny ears. In their early days, Walt Disney and animator U.B. Iwerks created a cartoon character called "Oswald the Lucky Rabbit." But the rights to the character were stolen from them, leading them to create a new character…Mickey Mouse. (Source)

Before she became a famous writer, P.L. Travers decided to up her name game. Her last name was originally "Goff." But after her beloved yet alcoholic father, Travers Goff, died of tuberculosis, she took his first name as her new last name. (Source)

Was this the inspiration for the Parent Trap—since it's kind of the same story, except way sadder? P.L. Travers adopted a boy named Camillus, but not the boy's identical twin. She never told him about his twin's existence—but one day, the twin showed up, in search of his brother. Travers turned him away, but Camillus tracked him down and reunited with his long lost brother in a London pub. (Source)