12 Biggest Retcons In Harry Potter Movies

8. The Hogwarts Express' Fifth Coach

You really have to be a bit of a know-it-all to spot this one, but here we are.

In the first five films, the Hogwarts Express train has four coaches, which isn't a great deal for the number of children at Hogwarts, but it presumably makes lots of trips that we just don't see or something. That's not a massively important plot-hole to be honest...

Anyway, in The Half Blood Prince, a fifth coach is mysteriously added and looks completely different to the others, as the story required a luggage rack for Harry to hide on to eavesdrop on Malfoy.

On top of that, throughout the series, the Hogwarts Express has the same iconic whistle apart from in the third film, in which - for no reason at all - a different whistle is used. Blame Alfonso Cuaron.