Continuity mistake: When Hedwig delivers the Nimbus 2000, as Harry catches it, the curve of the Nimbus' handle, the packaging and the way he grasps it all differ in the close-up and following shot. Then when Ron says, "Let's open it," he moves his goblet and plate to his left towards Hermione's goblet, yet in the next overhead shot his goblet is still on his right. (01:14:50)
Continuity mistake: During the scene with the troll, Hermione crawls over to where the sinks are and if you look at the floor you will see that there are only a few wet spots. In the very next shot, however, the whole floor is soaked (this occurs before the troll breaks all the sinks). (01:10:40)
Continuity mistake: After Harry opens the package with the invisibility cloak, he stands near the red chair and when he says, "I don't know, some kind of cloak," the cards on the back board are visible. As Ron says, "Well let's see then. Put it on," he holds a Bertie Botts box in his left hand and has his right hand in the box. Next shot facing Harry, Ron visibly holds the box with his right hand and the positions of the pillow, cushion, envelope and letter differ on the red chair. As the next shot opens facing Ron, he holds the box in his left hand and his right hand is in the box. Then in the next shot facing Harry again, the bottom card on the back board is gone. (01:27:50)
Continuity mistake: When we first see Hermione on the train, her tie is crooked. When she sits down, as Ron is about to change Scabbers yellow, her tie is straight and it remains that way while she is seated. When she leaves and turns around to tell Ron about the dirt on his nose, it is crooked again. (00:36:05)
Continuity mistake: When Harry receives his letter from Hogwarts, he opens it and it looks like one letter standard size. When the shot changes, it looks like a card (but we saw Harry unfold it). And when they are in London, right before they enter The Leaky Cauldron, it's standard size again but now there is more then one letter. Notice the folded left hand corner. (00:15:50 - 00:18:35)
Continuity mistake: In Harry's first Quidditch match, Gryffindor scores the first goal, then we see the commentator announce the goal and change Gryffindor's score to ten - making a goal worth ten points. Soon after, Gryffindor score again. We then see Slytherin score a goal, then another. They then score a third goal, and the commentator changes the score to 20 all, but it should be 20/30.