Continuity mistake: At his home, when Vernon says, "Fine day, Sunday. In my opinion best day of the week. Why is that Dudley?" in the close-up his arms are crossed right over left. In the next wide shot, as Harry answers, Vernon's arms are crossed left over right. Yet in the next close-up, his arms are crossed right over left again. (00:10:40)
Continuity mistake: When trapped in the Python exhibit at the zoo, Dudley stands up, presses his wet palms on the glass and nervously bangs on the glass while dripping plenty of water on it. However, in the next two shots after yelling, "Mummy, help! Help me!" the glass is all dry and just wet beneath his palms. (00:07:50)
Continuity mistake: When Hagrid and Harry step out the back door of the Leaky Cauldron, in the overhead shot there are many glass bottles on the floor, between the barrels. However, after Hagrid says, "Welcome Harry, to Diagon Alley," as they walk out the barrels are visible behind Hagrid and there are no glass bottles between the barrels. The stone ground differs in both shots too. (00:20:05)
Continuity mistake: In the scene straight after the Quidditch match where Harry, Hermione and Ron are telling Hagrid about their suspicions of Snape, you will see all three are wearing scarves tied in different ways. When there's a change of shots, the creases in the scarves change. This happens mostly with Hermione's. (01:23:55)
Continuity mistake: After Harry thanks Hagrid for his birthday cake, Hagrid sits on the couch. In the next two shots facing Hagrid as he pulls out his 'umbrella', Hagrid's fry pan suddenly lies on the couch, which is visible to his right. The way he pulls out the 'umbrella' and the position of the fry pan differ within the two shots. Moreover, the fry pan is gone after these two shots. (00:14:25)
Continuity mistake: After leaving Gringotts, Hagrid directs Harry to Ollivanders to buy his wand. When Hagrid says, "Why don't you run along there and wait...," there is a close-up of the store. Under the name Ollivanders the three roll window shades are completely pulled up, allowing the lamp chain to be visible behind the curved showcase window and the window shade at the top of the front door is pulled partially down behind the glass panes. However, as Harry opens the front door in the first shot, the window shades to his left, in the curved showcase window, are partially pulled down and the window shade on the door is now rolled up. (00:24:50)
Continuity mistake: In the scene where Harry and the Dursleys visit the zoo, the first shot you see of the snake, he is lying on a bare rock with only moss on it. He is also lying with his head facing the window, and his body is curving to the right. However, after Dudley walks away and the shot returns to the snake, his body is curving to the left and now there are plants directly behind him where there was only moss before. (00:06:00)
Continuity mistake: In the sea hut scene, when Dudley steals the cake, there's a shot of him eating it and his pyjama shirt is pulled up, then it cuts to Hagrid, and he says 'He'll be under the finest headmaster...' and it cuts back to Dudley, but his pyjama shirt is back down over his pyjama pants. (00:17:10)
Continuity mistake: While the first years are waiting at the top of the stairs just before being lead into the Great Hall for the first time, Ron's robes switch from being fully opened, to closed, then back again. (00:40:00)
Continuity mistake: When Hermione is saying to Harry and Ron "You won't make a fool of yourself, it's in your blood," Harry and Ron have several books with them, but straight after, right before the staircase moves, they have no books in their hands. (01:00:35)
Continuity mistake: On Dudley's birthday, when Mrs Dursley wakes Harry and he sits up in bed, a cloth and hand brush are hanging next to him on the inside of the cupboard door. When Dudley shoves Harry back into the cupboard, there is now a cloth and a dustpan, but no brush. When the family arrive back from the zoo, and Mr Dursley locks Harry in the cupboard, there is no cloth, brush or dustpan. (00:04:10)
Continuity mistake: At Kings Cross, just as Percy Weasley is about to run through the wall onto platform 9 3/4, we see a man and a woman walking past him, but when the shot changes direction, they have both disappeared. (00:31:15)
Continuity mistake: When Harry, Ron, and Hermione are heading to Hagrid's hut after discussing the stone, Harry says 'Why didn't I see it before?' his tie is all the way over to his right side, then when they are talking to Hagrid his tie is straight in the middle. (01:46:00)
Continuity mistake: When Harry raises his hand with the captured Snitch, his back faces the Slytherin and Hufflepuff towers which are opposite each other, with the hoops between them. However, in the next shot he is now facing that side of the pitch, as other Quidditch players appear from that side. (01:23:25)
Continuity mistake: The knotted tie string on Harry's Quidditch robe changes from extremely loose, to snug, to loose and so on, even in consecutive shots, from the time Harry speaks with Wood before they fly onto the pitch and throughout the match. This occurs with other members of both teams as well. (01:15:40)
Continuity mistake: When Petunia covers Dudley's face, her hands alternate from right over left to left over right. (00:05:30)
Continuity mistake: When Harry walks into the kitchen, Petunia tells him to take care of the breakfast and two of Dudley's presents, the blue design and the yellow, are visible on the couch. When Petunia asks, "Aren't they wonderful darling?" the camera pans the presents, including the ones from the earlier shot. When Vernon says, "Well some of them are quite a bit bigger than last year's," the two presents are again visible. The position of these gifts differs in all shots. (00:04:50)
Continuity mistake: When Uncle Vernon is nailing a small piece of board to the mail slot, he nails it angled slightly to the right. When Harry's letters start pouring in and the small piece of board is ripped from the door, it is angled slightly to the left. The actual wood boards differ as well. (00:09:55 - 00:12:00)
Continuity mistake: During Neville's ill-fated flying lesson, as he approaches the statue from behind, we see that the statue is placed atop a round turret with alternating levels of bricks around the top of the turret. Neville's robe then snags on the spear of the statue. When we see the front of the statue as Neville falls, the statue is now standing atop a flat, level section of wall. (00:56:55)
Continuity mistake: When Harry and Hagrid arrive in London and are speaking about what Harry needs to buy, the shot of them walking towards the camera has a block of three shops on their right. I cannot make out what the first one they pass is. The second is a cafe, and has the street no. 35 above it. The one nearest to the camera is a fruiterer/greengrocer ? numbered 33. Hagrid and Harry pass the first shop, and are outside the café. The shot cuts to Hagrid and he passes buildings with the numbers 45 and 44 on them (strange if the odd numbers are on the other side of the street). His head is just about to pass the no. 44 (maybe two steps more and he would pass it). We then cut back to Harry, who is walking past a wine shop ? not one of the three shops above. When we cut back to the shot of Hagrid, (after he has taken a few steps from the previous shot of him) his head is just about to pass the 44. (00:17:44)
Answer: Petunia or Vernon would have ran to a zoo employee and told them what happened. The employee would then open the door to the snake exhibit letting Dudley out.