Continuity mistake: When Laurie gets into Annie's car, she throws her coat in the back. During that shot when both of the girls are visible, the rear view mirror on the windshield between the two of them is level. When it cuts to only Annie and Laurie in the subsequent shots, the rear view mirror is crooked, tilting to one side.
Visible crew/equipment: At the end of the opening murder scene, when Michael's father takes Michael's mask off, you can see the shadow of the camera cast on Michael's father as it pulls away. (00:06:35)
Revealing mistake: When Annie is putting her clothes in the wash the door slams shut and she walks over to try and open it, look closely and you can see her turn the deadbolt and lock it so she can't open it. (00:46:45)
Continuity mistake: When Laurie escapes the house by smashing a window pane, the glass shards disappear instantly in the next shot. (01:17:47)
Visible crew/equipment: When Laurie tries to escape Michael from the kitchen, she breaks the glass. You can see a second hand break the glass in front of Laurie's.
Suggested correction: You are incorrect, but it's an understandable mistake to make because the scene is very dark. It's hard to see, but Laurie actually uses both hands to break the glass... she puts them together and then slaps them through the window in a quick, fluid motion. (If you go through frame-by-frame or in slow motion, it's much, much easier to see.) That's why you're seeing two hands. It's not a crew member's hand... it's Jamie Lee Curtis' other hand.
Continuity mistake: When Laurie goes to leave the key, the door has two intact glass frames but when the view changes there's only one that's almost completely broken. Later when Loomis enters the house, there's two again, with one only being slightly broken. Also, the frame from the inside looks really small when Michael watches, and we don't see planks nailed across to cut out the view from inside, as well as there being a screen door that isn't there from the outside, but is there when the view is from inside. (00:13:35 - 00:36:40)
Revealing mistake: Lynda calls Laurie using a rotary phone yet doesn't even look at what she's dialing. And you can tell she's not actually dialing in the first place.
Continuity mistake: At the start of the film Michael smashes the window, later on at the school the window is intact.
Continuity mistake: Michael breaks the passenger front door window on the wagon when he takes car, a short time later when he's driving in town the window is not broken.
Audio problem: While Lynda is filing her nails just as Michael enters the scene wearing a sheet and glasses, the sound of her filing continues despite her pausing.
Revealing mistake: Towards the end, Laurie pulls off Michael's mask, revealing his distorted face, but as he pulls the mask back down, the distorted face is also a mask as you can see the seam around his neckline.
Visible crew/equipment: When Bob gets impaled, Michael steps back to observe. Crew lights are quite visible behind Michael's head as the camera pans back. (01:05:50)
Visible crew/equipment: As Laurie heads up to the porch, the shadow of the boom is visible above the door.
Plot hole: Since the station wagon from the asylum was stolen, it should have been reported stolen along with the escape of Mike Myers. So why was the sheriff department not looking out for the stolen station wagon? We see Myers driving that station wagon freely without being stopped, while wearing a mask in broad daylight.
Continuity mistake: When Laurie, Annie and Lynda are walking home from school, the part where Lynda walks to her house you can see the station wagon on the side of the road behind them. A few seconds later it has moved up the side of the street.
Revealing mistake: When Tommy is trying to show Laurie that Michael is outside, something to the left of the Wallace house looks like legs moving around in the dark and then jumping up. Presumably, this is Nancy Kynes jumping up into Tony Moran's arms so that he can carry her around the front of the house, which is actually the shot that is used about ten minutes later. Carpenter potentially used this shot of the house either unaware that they could be seen, or didn't anticipate the future change in aspect ratio. (00:45:30 - 00:55:30)
Deliberate mistake: In the first scene of the movie, we soon realize that we are looking at a house from someone's point of view who has no trouble looking over a porch railing, about 6 feet above the ground. It's revealed later that he is a little kid, about 4 feet tall. John Carpenter deliberately filmed it that way to exaggerate the impact of his little kid killer reveal. Unfortunately, when the kid is standing outside the house with his parents, you can see he could never have looked over the porch railing.
Continuity mistake: Michael is watching Annie in the kitchen. He knocks down the hanging plant in front of the door and it shatters. When Laurie goes to check on her she goes in the same door and the plant is hanging back up. (00:43:21 - 01:12:56)
Continuity mistake: The scene of Dr Loomis talking to Michael in his room, scene from the TV cut, shows him sitting in a chair his arms down at his sides. A shot of Loomis then back to Michael show his hands on his knees. Another shot of Loomis then Michael shows his left hand still on his knee but now his right arm's down at his side.
Audio problem: When Laurie's crying near the end her mouth isn't moving in sync with the audio.
