The Magical Travel Mistake In Harry Potter And The Goblet Of Fire

In Chamber of Secrets, Rowling makes it very clear that floo powder only works if every witch or wizard takes some, stands in the fireplace, and says the name of the place they want to go. Things break down for Harry Potter in that book because he doesn't say the name of the place he wants to go right.

In Goblet of Fire, though, when the Weasleys pick Harry up from the Dursleys' at Number 4 Privet Drive to take him to the Quidditch World Cup, the rules of floo powder seem to change slightly. As the Weasley family prepares to leave, Arthur puts a dab of floo powder in the fireplace that allows them all to travel back to the Burrow. After Arthur puts the floo powder in, the rest of the Weasleys just have to step into the fireplace to get transported back to the Burrow, without taking powder themselves or saying where they want to go.

This change is a break from the rules in Chamber of Secrets, where everyone has to arrange their own travel with floo powder by themselves. It's a shorthand that allows for Rowling to avoid explaining the rules of floo powder again, but one that bothers diehard fans obsessed with the intricacies of her magical world.