Continuity mistake: Notice how Michael is taking/reacting to being hit by the bullets at the conclusion of the first Halloween - you see him writhe in pain, his hand shake and grab near his side, and his body contort and literally twist before falling off the balcony - a believable shooting death scene. When the scene was re-enacted at the beginning of part II, all Michael does is lazily walk backwards and fall off.
Revealing mistake: When Doctor Loomis touches the blood in the beginning, you can see a bit of material (it appears to be plastic) sticking to his fingers as he pulls them up from the grass. It appears as though it was somehow involved in the effect of him touching the blood. (Perhaps to keep it from soaking into the ground?).
Plot hole: In the first scene Alice hears on the radio that three teenagers had been murdered in Haddonfield just down the street from where they live. Yet a few scenes later, the sheriff finds out from his deputy that 3 bodies have been found. Wouldn't the police department know that before it made its way onto the radio news?
Continuity mistake: When Loomis thinks he sees Michael but it is actually a drunk Ben Tramer in a mask, he runs after Tramer and pulls his gun. Brackett sees this and runs out of his patrol car, slams the door, and stops Loomis before Loomis gets off a shot. A few seconds later though, the car door is now open in the background.
Continuity mistake: When Michael stabs Nurse Jill in the back with the scalpel and lifts her off the ground, her shoes fall to the floor. A few seconds later, they are rearranged differently on the floor.
Continuity mistake: After the explosion and Michael is walking on fire, you'll notice he is right next to the burning stretcher. Then they cut to a scene of Laurie hiding behind a water fountain. In the next scene of Michael, he is now about 8 feet behind the stretcher walking towards her again.
Continuity mistake: Near the film's climax, the marshall is shown walking down a hallway by a soda machine and reacts to Laurie's screaming. He then makes a turn around to go see what was up. Several seconds (and many screams) later, Michael crashes through the door and the marshall is still running down the hallway by the same soda machine.
Continuity mistake: In the original film, the pumpkin at the Wallace's house was very small and fat, but in this film (which takes place the same night) you can see when all the cops and reporters are at the house that the pumpkin changed in size and the face is different as well.
Other mistake: When Bud goes to check on how hot the water is, he rubs condensation off the gauges, but there wasn't anything on them to begin with.
Continuity mistake: When nurse Karen first enters the hospital and changes into her uniform, she's clearly shown putting on a dark belt (either black or brown). However, in her next scene with Mrs. Alves, as well as the scene where she's tricked into entering the hospital room to fool around with Bud, the belt is white.
Plot hole: Laurie is pounding on the door and screaming for help. But Loomis doesn't hear her for a full 20 seconds? It even shows him standing 30 feet from the door and he doesn't come running until Laurie has screamed for 20 seconds.
Continuity mistake: When Laurie leaves the hospital, she exits out of the hospital doors. Somehow the doors stay open. Later on in the far away shot, the doors are closed, then they are open again in the next shot.
Continuity mistake: Towards the end of the film, when Dr. Loomis finally finds out Michael is at the hospital and orders the trooper's car to turn around. As the car turns around, the lighting outside appears to be pre-dawn however they arrive at hospital and it is still pitch black.
Continuity mistake: When Pamela Susan Shoop is being killed by Michael in the spa, the towel is tied arround her upper chest, then the towel falls down, revealing her breasts. In the next shot a split second later the towel is back up at he upper chest.
Revealing mistake: At the end of the film, when Michael Myers is on fire walking out of the room in the hospital towards Laurie one can see that he is wearing gloves (probably so the actor will not be burned), but during the course of the entire movie, Michael Myers' hands are always visible.
Continuity mistake: At the end of part one, Laurie's stab wound was just a streak of blood and none on her shirt at all. When they bring her out to the ambulance, there's now a lot of blood on her shirt and streaks of blood on her arm. (00:13:20)
Factual error: When Michael corners Laurie in the elevator, the door shuts just in time and slams on his hand and just keeps closing, and Michael pulls away. Elevators have rubber guards that would cause the door to open again if someone's hand would get caught in the closing.
Continuity mistake: After getting out of the car, Laurie is on the ground beside Jimmy's car outside the hospital when she sees the Marshall's car pull up. When Loomis tells the Marshall he ought to handcuff him to the wheel, if you look, Jimmy's car is still visible in the distance, but Laurie is not in that shot.