While in the company of Tommy Doyle, Laurie places the keys to the Myers' house under the mat at her father's request. Tommy says goodbye until later that night and Laurie starts singing to herself walking down the street. Michael Myers then watches her, breathing heavily but the motions of his chest and shoulders rising and falling do not match the sound.
In the beginning of the movie Michael is six years old. The rest of the movie is enacted 15 years later, so Michael must be 21 years old. In the end credits however, there's a Michael of age six and a Michael of age 23.
When Annie brings Lindsey Wallace over to the Doyle house, she tells Laurie that she will just have to call Ben Tramer "tomorrow." In actuality, Laurie could just talk to Ben at school, as November 1, 1978 was on a Wednesday.
Annie moans about having to babysit at the Wallace's house, and Laurie says she's babysitting at the Doyle's home which is three houses down. Later in the movie the Wallace's house is shown to be across the street from the Doyle's.
When Michael Myers, as a child, walks through the living room with the knife, the clock above the stove shows 9:25 and the clock on the wall reads 9:40, but just 5-7 seconds later, the clock chimes 10 times.
When Laurie walks to the Myers house to drop off the key, she only has a few blocks to walk. However, when she and Annie drive clear across town to reach the Doyle house, the Myers house is conveniently close by.
When Annie is first shown spilling something on her clothes and takes them off to wash them, her panties are a solid color. Later when she is in the laundry room her panties have flower prints on them.
In one scene, Lindsay is alone watching television. The sounds coming from the movie indicate that she's watching a later scene from Howard Hawk's "The Thing." Several scenes later, just before Lindsay is dropped off to Laurie Strode's house by Annie, Laurie and Tommy are watching television and "The Thing" is just coming on.
When Laurie and Annie are walking down the sidewalk and Laurie
sees Michael standing next to a bush, from Laurie's point of view the bush is trimmed and neat, but when Annie walks up to the bush, it's all bushy with leaves sticking out everywhere.
Whenever Laurie, Tommy or Lindsey looks out the window at the Wallace House, there is a pumpkin visible with a candle burning. In all of the shots except two, the jack-o-lantern is a flat-looking thing. The two exception shots show a tall and more narrow/skinny pumpkin.
After Doctor Loomis has talked to the Sheriff from a phone on the highway and warned him about Michael, he notices a red pick-up truck and walks towards it to inspect it. We can hear the noise from the train that is coming towards the camera on the left side, shows up and starts to pass. The next shot, is from the opposite side, showing the Doctor and the truck from the front. We still can hear the train passing but there is no train in the background.
Toward the beginning of the movie when Michael is attacking the woman in the car, she steps on the gas turning the car toward some trees. In the next scene when she jumps out of the car, Michael jumps in and drives off. The trees aren't there anymore and he's driving straight on a road.
When Michael is watching Annie in the kitchen he knocks down and breaks the plant hanging in front of the door. Later when Laurie approaches the same door there is a plant hanging in front of the door.
As Laurie is walking home from school, a leaf (or some other debris) is briefly seen stuck in her hair. When she turns back, looking towards where Michael was after she bumps into the Sheriff and is startled, the leaf is gone.
After Lynda says goodbye, Laurie and Annie continue to walk home from classes together and the following scenes show that the takes were combined from different periods of the day. When Laurie sees the Shape peering at them behind the bushes, the Sun is setting behind the houses to their left. In the very next scene when she tries get Annie's attention, the Sun is shining on them from directly above. When Annie rushes to confront the Shape the Sun is still setting but once Annie departs, it shines completely overhead again as Laurie is frightened by Sheriff Brackett.
After Judith's boyfriend leaves, young Michael ascends the steps to his sister's bedroom with a kitchen knife in hand. Her clothes are balled up together in a pile on the floor at the top of the landing. After he picks up the clown mask from the ground and puts it on, the pile of clothes are now trailing piece by piece towards Judith's bedroom door and one of the articles, a pink sweater, is now openly lying flat.
When Laurie first arrives home from school, she glances out the window and sees Michael standing in her neighbor's yard. It is very windy. But in the next moment, she slams the window shut and the trees are perfectly still.
When The Shape attacks Laurie while she is hiding in the closet, the position of the clothes, as well as the types of clothing hanging in there, change frequently, and in every shot of the closet afterwards.
When Annie and Laurie are driving in the burgundy 1977 Monte Carlo, the rear view mirror changes from being perfectly straight to being crooked. Almost every other scene the mirror is the opposite of the scene prior.
When Dr. Loomis is talking in a phone booth after Myers escapes ("It's your funeral!"), when he exits the booth and notices the abandoned truck, a crew member is reflected in the glass of the phone booth.
When Annie is by the hedgerow telling Laurie that the person who has been following them wants to talk to her, a puff of John Carpenter's cigarette smoke floats into the shot. (This was pointed out by Carpenter during the film's audio commentary)
The scene that shows Laurie, Annie and Lynda walking home from school starts with them walking from a school with outside lockers, schools with inclement weather, such as Illinois, do not have outside lockers.
When Lynda and Bob pull up to Lindsey's house, you can clearly see a California license plate on the front of the van. (blue with yellow numbers). Other vehicles in the film have the proper Illinois plates (white with black numbers).
Annie tells Laurie that she will pick her up at 6:30. When she does, it is full daylight, which is not the case anywhere in Illinois on October 31. And even though it is a small town, it's full dark when the girls arrive at their destination.
At the beginning of the movie Michael is supposed to be 6 years old. However, when he is walking around the house you can clearly see that the scene is being shot by an adult. The camera is well above the door knob and when he goes outside he is as tall as his parents. Then they take the mask off and the view switches to the long scene, notice how much shorter than the adults he is.
Filmed in the spring in California, pumpkins were not in season and the low budget of the movie ruled out creating artificial varieties. Most of the pumpkins and jack-o-lanterns seen are squashes painted orange. As a result they often look somewhat flat or misshapen with the wrong textured skin.
(Extended version) Dr. Loomis and a nurse from the Smith's Grove Sanitarium walk down the hall and discuss who was supposed to be watching Michael Myers when he escaped and the camera pans down to Dr. Loomis' loafers as they enter the destroyed room. In the next scene, walking to his car with Dr. Wynn, Dr. Loomis is clearly wearing brown dress shoes that click as he walk - something the loafers did not do in the previous scene.
Autumn leaves cascade down on Laurie and rustle to the ground as she exits her house in expectation of Annie to pick her up. As she sits at the corner watching children trick-or-treat there are no leaves falling anywhere else in the neighborhood, not even to her immediate right side where the lawn and sidewalk are clean.
The date on the tombstone above Annie says that Judith Myers was born November 10, 1947, and died October 31, 1963. That would make her 15 (almost 16) when she died, yet everyone says that she was 17 years old.
After Michael has killed Annie, he carries her body around the side of the house. In the first shot, notice her head is to the left side of Michael's body and her feet are on the right side. It then cuts to Tommy who is watching from the window across the street. When it cuts back to Michael carrying Annie up the front steps of the house, her body has switched positions. Her head is now on the right side of Michael and her feet on the left.
When Laurie jabs the needle in Michael's neck, he sticks the butcher knife in the couch. After Michael falls, Laurie picks the knife up, looks at it, and then throws it on the floor next to the couch. Later, Michael comes upstairs holding the knife. Before the end credits, when we hear Michael breathing and it shows all the shots of the house, the knife is still on the floor next to the couch.
After Michael has stabbed Judith, his sister, he leaves the house and when the camera pans upward, all the lights in the house are on. But, they were never on when Michael was inside and he never turned them all on when he was exiting the house.
After Michael goes upstairs to kill Laurie and the children, Laurie tells the kids to lock themselves in the bathroom in the bedroom, and she herself goes into the closet. Before Michael comes up, she knocked on the door of the bedroom to let the kids know she was okay, so why didn't she lock the bedroom door when she and the kids hid? Michael left them enough time for her to barricade herself and the children in the room, and she could have easily closed the door and locked it.
When Michael stabs Bob with the butcher knife, the knife goes all of the way through Bob and into the wall. However, the knife is barely even long enough to go entirely through Bob's body (if at all), much less the additional length required for it to be deep enough in the wall to hold up his weight.