brassmaster

Revealing mistake: When Hermione fakes reading the crystal ball, Trelawney insults her and Hermione knocks the crystal ball off the table. As the crystal ball leaves its stand it turns over and the tube used to create the smoke effect inside the ball is visible. Then as the ball rolls toward the stairs, there are no tubes visible. (01:19:55)

Revealing mistake: In the scene in which Harry, under the guise of the Invisibility Cloak, is dragged by the Weasley twins into the castle by his arms, it's obvious that the twins are miming a person in between them. There is one point when they round the corner right before throwing him onto the stairs, the twins are pretty much side by side, there is absolutely no room between them for a person at that point. They then widen the space again right after they round the corner. (00:56:55)

Revealing mistake: When Ron and Hermione are arguing with Malfoy near the Shrieking Shack, Malfoy visibly flinches before he is hit by the first snowball. He's not looking in the right direction to see it coming. (01:02:15)