Visible crew/equipment: During the Quidditch match Harry's broomstick tries to shake him off, due to the spell. After Hermione tells Ron, "Leave it to me," in Harry's last close-up before he flips over, the seat that is attached to the broomstick, to make it more comfortable for Dan Radcliffe to sit on, is entirely visible. Glimpses of other seats can be had during the match as well.
Other mistake: When Harry receives his first letter in the mail, Dudley snatches it from him before he has a chance to open it. Then he gives it to his father (Uncle Vernon), and Uncle Vernon says "Who'd be writing to you?" If you watch Dudley carefully, you can see him mouth what Uncle Vernon is saying.
Visible crew/equipment: In the scene where Hermione, Ron and Harry are returning to Gryffindor's tower room after being in the third floor room for the first time, you are able to see the feet of one of the crew. It happens just as they are passing through the picture hole, where Harry turns a couple of times to check that the "door" is closing. And it is in fact, because someone is walking behind it and pushing it shut, since the picture hangs several inches off the floor.
Visible crew/equipment: Being chased by the flying keys, as Harry zips by on the broomstick he tosses the key, Hermione catches it and runs to the door. In the next shot, a close-up, as she tries to unlock the door, an electrical cable hangs down beside the column, that was not in the previous shots. There is also an electrical cable coming out from under the back of Hermione's sweater that is blatantly visible as well.
Continuity mistake: When the troll enters the girls' lavatory, in the wide shot as Hermione walks backwards towards the cubicles, the room becomes brighter from the storm. With this extra bright light it is simple to see that the wall between the 2nd & 3rd cubicles actually touches the floor, unlike the other cubicle walls. Yet, in the overhead shot as the troll's club slams into the cubicles, Hermione is lying under that very wall crawling away. Impossible!
Visible crew/equipment: At the Quidditch match, after Hermione sets Snape's cloak on fire and someone shouts, "Fire! You're on fire!" there is a close-up of Harry with his hands gripping the Nimbus 2000. In this shot, the wire rods which are attached/taped to the broomstick, near Harry's fingers, that lead under both of his red sleeves, are entirely visible.
Visible crew/equipment: Petunia has her hands on Dudley's eyes as they walk towards all of his birthday gifts. When she removes her hands from Dudley's eyes, in this shot and in the next, the long black microphone wire as well as its tape, which obviously peeled free, are blatantly visible and are sticking out at the neckline of her v-neck top under the pearl necklace. It's gone in the following shots. (Do not confuse the blue apron strings for the mic wire.)
Visible crew/equipment: While at the zoo, after Dudley falls into the snake exhibit there is a close-up of the Python's head. At the start of this shot, before Dudley pops out of the water, in the upper left corner of the screen a wood stick comes down to actually prod the trained snake and then quickly moves back up out of shot! (DVD fullscreen for best visibility.)
Continuity mistake: At the snake exhibit, while Harry speaks with the Python the snake's body lies curled over a long wood log and a large rock. In the shot from outside the Python's exhibit, after the glass pane disappears Dudley falls over the rail and the snake is gone, not positioned differently, but altogether gone! In the next overhead shot inside the Python's exhibit, while Dudley falls the snake is back lying on the log and rock, in the same position as in the previous shots.
Visible crew/equipment: Hermione opens the door to Fluffy's room when she says, "Alohomora!" so she, Harry and Ron could hide from Filch and Mrs. Norris. As Ron closes the door the top of the third floor corridor set is visible at the top of the screen. As an aside, when Ron repeats, "Alohomora!" look at Hermione's face!
Visible crew/equipment: During the Quidditch match as the players ride their broomsticks, visible in quite a few shots are the two wires that are attached to the broom handle, between their legs, that extend down with a clamped loop that goes around their feet. In some shots the wires between their legs are edited, but the wire loops around their feet are perfectly visible, like in the following example. When the Slytherin score hits 10 onscreen, in the next shot, as Flint shouts, "Take that side," the wire is completely visible at his right foot under his cloak. Two examples where the entire wires are visible are, when Flint grabs the club and says, "Gimme that!" the wires are blatantly visible and he then proceeds to slam the Bludger into Wood, who falls. Next close-up of one of the twins, the wires are visible before Flint starts to leap over him. (Don't confuse the cloak's long front ties for the wire).
Continuity mistake: Dumbledore, McGonagall and Hagrid leave baby Harry on the Dursley's doorstep. When the shot opens in the first close-up of the baby, as Dumbledore places the envelope on the blanket, though a good portion of his forehead is visible, the scar is not there. In his next close-up, it is very apparent, due to the position of the scar, that part of it should have been visible on his forehead in the previous close-up.
Visible crew/equipment: Petunia and Dudley enter the house when they return from the zoo, followed by Vernon and Harry. The crew's equipment is plainly visible on the ground beyond the doorway. Also, the pavement at the threshold extends far beyond the doorway and just before Vernon walks into the house, Vernon is visibly coming from the side of the doorway. In the earlier exterior shot when they stand by the car before they leave, as Vernon says, "I'm warning you now boy...," not only is the ground at the doorway completely different, there is a garden surrounded by white bricks beside the door, making it impossible for Vernon to have been standing there. (Visible on DVD fullscreen.)