Continuity mistake: After Dudley shouts, "Wake up, Potter! We're going to the zoo," he pushes Harry back into the cupboard and runs into the kitchen. When he opens the door, the kitchen floor is visible and there are no floor mats. Yet, once Harry walks into the kitchen there is a taped black mat on the floor at the door and another black mat at the counter, under the stools that were visible in the previous shot, when Petunia bangs on the cupboard door. (This does not refer to the reddish mat Dudley stands on.) (00:04:35)
Continuity mistake: When Harry and Hagrid walk into Diagon Alley, in the first shot, as they start down the street, on their right they immediately pass; 1- a man in black standing at the doorway to the Daily Prophet office, writing in a notebook, who then starts to walk away. 2- particular men and women walking past the store. 3- store window with Quidditch uniforms. 4- children looking in store window. A few shots later, they pass on their right a man, with bushy grey sideburns, walking with a woman dressed in black, yet in the next shot that same man and woman are chatting in the doorway to the Owl Emporium on their left. Then a few shots after that, still walking, Harry and Hagrid pass all the numbers, 1 through 4 again in close-up. (00:20:40)
Continuity mistake: The morning of Dudley's birthday, Petunia wakes Harry and the next shot shows Harry in the cupboard with the shelves behind him. When Dudley runs downstairs and pushes Harry back into the cupboard, things inside are positioned differently. This also occurs in the two shots when Harry plays with the small plastic figures inside the cupboard and then when he peeks out as Vernon attaches the wood to the mail slot. (00:04:20)
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)
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)
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)
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)
Continuity mistake: Harry speaks with Quirrell near the Mirror of Erised and the arrangement of the cloth in his turban differs in two shots than in the rest of the shots. First in the shot facing Harry as Quirrell says, "While everyone else was running about the dungeon, he went to the third floor to head me off," and then in the back shot just before Quirrell unwraps the turban, after Voldemort says, "I have strength enough for this." (02:08:05 - 02:09:45)
Continuity mistake: When Dudley falls into the water in the Python's exhibit, his clothes are completely soaked. Yet when Dudley yells and bangs on the glass, in the shot facing Petunia as she screams, it is quite apparent that Dudley's sweater/jumper is not entirely wet. The wet hair at the back of his head lies flat in the second shot as well. (00:07:15)
Continuity mistake: After Seamus' disaster with the rum spell, the mail arrives. Ron catches his mail, then holds the Daily Prophet in his right hand and the letters in his left. Yet in the next close-up he holds the Daily Prophet in his left hand and the letters in his right. (00:54:05)