Revealing mistake: While Vernon kneels as he tosses Harry's Hogwarts letters into the fire, the interior solid back of the fireplace is visible behind the flames. On Sunday, the first letter (from the fireplace with a CG back) hits Vernon in the face as it flies by. In the following two shots of the fireplace, as more letters fly out, there are now large holes at the interior back of the fireplace that are visible. As the letters pour down from above, air is blown through these holes to blow the letters out and about. (00:10:20 - 00:11:20)
Continuity mistake: When Snape enters the classroom during the first Potions class, there is a lit candle and an hourglass on the desk directly behind him. But in the following shots the candle and hourglass change positions and move farther away.
Continuity mistake: As Hagrid aims his 'umbrella' at Dudley while he eats Harry's birthday cake, in the side shot one end of the blue string (that was tied around the cake box) hangs down the side of the table, but when Vernon rushes Petunia and Dudley off, in this shot that end of the string lies on top of the table. Yet, when Hagrid says, "We're a bit behind schedule. Best be off," the string hangs off the side again. (00:17:30)
Revealing mistake: Just after Harry gets back on his broom, the Slytherine seeker chases the snitch and he passes towers of (in order) Gryffindor, Hufflepuff, Ravenclaw, Slytherine, Gryffindor and Hufflepuff, on his left (this means Hogwarts is also to his left), when Harry flies up beside him. However, next shot as Harry slams into him, they still fly in the same direction, and the school is now on their right. Mistake with the background plate. (01:22:00)
Continuity mistake: The size and style of the writing on the envelope from Hogwarts at the starts changes depending on the shot. When Uncle Vernon picks it up, the word "stairs" is a fair way from the edge of the envelope. When he flips it over and you get a close up, the same word is a lot closer to the edge. (00:08:50)
Continuity mistake: When Harry lifts the mail from the floor at the Dursleys, the Hogwarts envelope flap is sealed shut and it has the red wax seal at the tip. Yet in the kitchen after he hands Vernon the other letters, Harry holds the Hogwarts envelope and though the red seal is on the back, the flap itself is NOT sealed shut. The wax seals differ in both shots as well. (00:08:45)
Continuity mistake: As Hermione walks toward the troll, just before she asks, "Is it dead?" the long towel hanging from the rod beside the sinks is visibly straight. When Harry lifts his wand with troll booger/bogey, in the shot of him as he grimaces and groans, the towel on the rod is visible behind him and it's messy. Yet when McGonagall, Snape and Quirrell walk in, the long towel is straight again. (01:12:00)
Audio problem: When Hedwig flies from Harry's arm, or owls deliver mail, you hear the sound of wingbeats. However, owl's feathers are specially adapted to allow for completely silent flight. See here for an explanation. http://www.owlpages.com/articles.php?section=Owl+Physiology&title=Feathers. (00:53:45)
Continuity mistake: When Madame Hooch leaves with Neville to go to the hospital wing, Seamus holds his broomstick with the bristles on the ground as Malfoy ridicules Neville. However, as Malfoy steps on his broomstick and then flies away, the bristles on Seamus' broomstick are now at the top. Then when Harry takes off on his broomstick, the bristles on Seamus' broom are on the ground once again. (00:57:30)
Continuity mistake: When Malfoy first talks, the window behind him is bright blue. He says "it's true then, what they are saying on the train, Harry Potter has come to Hogwarts." Everyone says "Harry Potter" and when it cuts back to Malfoy, the window is much much darker. Both a mistake in terms of continuity between windows, and also a mistake because we'd seen everyone turn up in total darkness earlier, so the window shouldn't have been lit in the first place. (00:40:30)
Revealing mistake: After Madame Hooch takes Neville to the hospital wing, Malfoy takes the Remembrall and mounts his broomstick, on a convenient protruding metal rod. Then when he comes around, though the students step away and watch as he begins to fly off, many of their eyes are not level with Malfoy, as he is merely edited into the end of this shot. (00:57:50)
Continuity mistake: At the end-of-the-year feast the Slytherin banner is green and gold, but their house colors are green and sliver, as evident by their robes.
Continuity mistake: At the hut on the rock, Harry lies on a grey blanket spread on the ground between the fireplace and the couch. When Hagrid bangs on the door, Harry quickly jumps up and hides, leaving the blanket behind. Though the blanket is visible on the ground, in some shots, it is however, gone in the three wide shots with the Hagrid body double, as he zaps a tail on Dudley, then as all the Dursleys run upstairs, as well as the shot after Hagrid says, "We're a bit behind schedule, best be off." (00:12:55)
Continuity mistake: After shopping in Diagon Alley, when Harry confronts Hagrid about Voldemort, in the first overhead wide shot Hedwig's cage is right next to Hagrid on the bench and is positioned a particular way. Yet in the next shot, the cage is much farther from Hagrid and is positioned the opposite way on the bench. (00:28:45)