It's been in cinemas for less than a week but already mistakes have been spotted in The Prisoner of Azkaban.
A movie mistake website has listed 12 blunders that have so far been spotted by eagle-eyed Potter fans.
The mistakes posted on the site mostly relate to the continuity of the film - that means things changing between scenes when they shouldn't.
One post mentions a scene in Lupin's office. The Marauder's Map is placed on a table, but then it disappears!
Another fan says that when Hermione punches Malfoy, she spins round and hits him all in one motion.
However, when Harry and Hermione watch themselves later, Hermione is already facing Malfoy when she punches him.
Even the Newsround team think they may have spotted a slip-up.
When Hermione takes the Time Turner out from her top on a chain, it looks like a small chain.
But then she wraps it around herself AND Harry, and it's really long.
If she had that long chain around her neck it would've been dangling down by her feet!
When Harry thought he saw his dad save him (it was really himself) there was a shape of a deer but when Harry went back in time it was not there.
William, 9, Barnsley
In the scene with Buckbeak the camera is close on Ron and he's clapping his HANDS for Harry, however, when the camera moves back on Harry, you can see Ron clapping one hand on his BOOK instead.
Elle, 15, Lexington
I spotted a mistake when Snape caught Harry in school in the middle of the night - Lupin came and took Harry to his office when out of the windows it was bright and sunny!
Anna, 12, Norwich
When Harry is under his invisibility cloak his eyes are green, but then when the camera goes back on him, his eyes suddenly return to blue.
Amy, 15, Dallas
When the trio are in Hagrid's hut before Buckbeak's beheading, a pebble (thrown by who we later find to be Hermione) hits the ceramic vase on the table, which breaks, leaving half of it standing up. Later, when Harry and Hermione revisit this moment in time, Hermione throws the pebble, hitting the vase, but this time when it shatters no piece is left standing up.
In the scene where Harry is confronted by Snape when he's "sleep walking" Harry is holding the map one handed but the close-up shows him holding the map with two hands.
Martin, 14, Essex
When filming in the Shrieking shack, whenever Harry (Daniel Radcliffe) went to say his line, you could see Hermione (Emma Watson) mouthing it!
Katie, 12, Kent
I saw a mistake, it was when Harry looked at the poster of Sirius Black. The first time the number was 390 and the second it was 007.
Alana, 10, East Cowes
When Harry and Hermione are back in time, toward the end of that period, before they were attacked by Moony, you can clearly hear Alfonso say "Emma" then Emma/Hermione walks out of view then you can here her say "what ?".
Spike, 14, Rotherham
Hermione wraps the chain twice around her neck, so it's not long around her neck but it is when she unravels it.
Juliet, 16, Norwich
At the start of the film when Harry blows up Aunt Marge it is light, but when he storms out it's night time.
I spotted a mistake - near the beginning, Harry's scar changes sides from right to left then back again.