Visible crew/equipment: Harry gives Vernon two letters and he walks to the other end of the table to open the Hogwarts envelope. When Dudley grabs the letter, as he shouts, "Dad look! Harry's got a letter!" under Dudley's chair, to the left, the black tape mark is visible on the carpet covering. The carpet is covered over near Dudley's chair and on the other side of Vernon, near the black mat. In the close-up of the letter as Vernon holds it, the carpet is back to normal near Dudley's chair. (00:09:10)
Visible crew/equipment: When Hagrid enters the hut on the rock, as well as when he leaves, the bare floor near the front door is clearly visible. However, when he says, "It's not everyday your young man turns eleven, now is it?" in the next shot as Hagrid sits down, on the floor to his left is the crew's mat with marks for the Dursleys (Fiona Shaw and Richard Griffiths), who stand near the door. (00:14:25)
Visible crew/equipment: On the Hogwarts Express, as Ron says, "This is Scabbers by the way," the acrylic string/wire which is attached to the bottom of Bertie Botts box, that is over Scabber's head, is perfectly visible. (00:36:05)
Visible crew/equipment: In the opening shot at the hut on the rock, when the camera pans down to Harry lying on the floor the long marks that are taped to the floor near the couch are visible. These are the positions of Vernon and Petunia when confronting Hagrid about Hogwarts. (Visible on DVD fullscreen.) (00:12:25 - 00:16:30)
Visible crew/equipment: When Harry and Hagrid walk down Diagon Alley, in the close-up of Quality Quidditch Supplies, a clear reflection of a crew member in a blue shirt is visible, at the top of the screen in the hanging vertical pennant, just as the man with the long red hair walks past the camera. (Visible on DVD fullscreen.) (00:21:20)
Visible crew/equipment: When Harry, Hermione and Ron reach the common room, on their way to the trap door, they're confronted by Neville, who asks, "You're sneaking out again, aren't you?" In the wide shot as Harry says, "Now Neville, listen...," Rupert Grint's (Ron) tape mark is visible at his feet. (01:53:35)
Visible crew/equipment: The morning of Dudley's birthday, in the wide shot facing the kitchen when Harry walks in, to the right of the screen is a large framed photo of Dudley. The camera does not move as Harry walks toward the stove and reflected in that photo is a piece of studio equipment moving. (00:04:50)
Visible crew/equipment: When Malfoy steps onto his broom while holding Neville's Remembrall, the actor's two curved chalk marks can be seen on the ground near Hermione's feet, and just as Harry steps backward we can see the actor's chalk marks on the ground near his feet. (Fullscreen version). (00:57:30)
Visible crew/equipment: In the very beginning of the movie, Dumbledore is walking along Privet Drive. There is a shot of him walking past some trees. When he does this, you can see his shadow flat across the background. The trees are obviously a painted set prop. (00:00:35)
Visible crew/equipment: In the scene where Harry and Ron come running down the hallway and see the troll for the first time, you can see a floodlight at the top of the frame illuminating the area where they stop and hide. (01:09:30)
Visible crew/equipment: When Oliver Wood is explaining Quidditch to Harry, he struggles to put the Bludger back in the trunk. You can see a rod under the trunk lift and shake it, so the Bludgers appear to be moving on their own. (01:05:55)
Visible crew/equipment: Hagrid surprises Harry with the box of birthday cake and Harry opens the box. In the close-up of the cake, as Harry holds the box with his left hand and moves the blue string with his right hand, a crew member's finger is visible under the box, over Harry's left shoulder. Obviously it is someone holding the box underneath, while Harry holds it with one hand. (00:14:10)
Visible crew/equipment: In the scene where Harry is left on the door step, when Dumbledore puts Harry down to the right of him the blue screen is visible. (00:03:20)
Visible crew/equipment: After entering the Key room Harry says, "They're not birds... I'll bet one of them fits that door," and as they reach the levitating broomstick, at the bottom right corner of the screen, the shadow of the overhead boom mic moves on the floor. (01:58:20)
Visible crew/equipment: When Harry, Ron, and Hermione are struggling in the Devil's Snare, a puppeteer can be seen on the left of the screen, working at least some of the masses of tendrils. (01:52:00)
Visible crew/equipment: As the first years amass at the top of the steps prior to being sorted, a strong, round white light is in the glass behind McGonigal. (00:38:10)
Visible crew/equipment: When Dumbledore gives the order to the students to follow the Prefects towards their dorms after the troll came out from the dungeon, just a moment before Harry warns Ron that Hermione is unaware of what is happening, some light reflectors simulating lightning are reflected on the glass above the pathway where the students come from. (01:05:55)
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.