When Mike pulls the car up the driveway, he pulls the lever wearing blue pants, but when he steps out, his pants are brown.
(at around 56 mins) The Volkswagen originally faces the overturned ice cream truck, but when Mike breaks through the back window and the car takes off, the ice cream truck has disappeared.
(at around 1h 2 mins) When Mike is trapped in the Tall Man's hearse, he shoots at the right rear tire to make it crash, but the left rear tire is shown blowing off of the car.
Glass in the broken window changes through the movie.
When the Caretaker's head is bored into by the orb, there's no blood near his fallen body.
(at around 10 mins) Early in the movie after Jody and Michael return from joyriding, Jody's friend Toby pulls up outside the house and Jody asks him what brings him to town. Just a couple of scenes earlier, Toby and Jody can both be seen lifting Tommy's casket from the hearse because they were both pallbearers at Tommy's funeral. However, this scene was a flashback showing how Mike found out that Jody was going to be leaving and could have taken place before the funeral.
(at around 41 mins) When the finger-turned-bug flies out of the garbage disposal and passes Reggie's head, the string used to pull the bug is visible.
When Jody inserts a screwdriver into his brother's door, the length of the shaft and the angle he wedged it in would have made the tip go into the room. Firstly, that doesn't create a very effective wedge lock. Secondly, it would have been easy for Mike to take the hammer he so clearly has and merely tap the tip of the screwdriver that should have been on his side of the door. The screwdriver would have popped right out, or at least dislodged enough for him to open the door.
When Mike jumps out of the car, his landing is too easy. Jumping out of a moving car would have been a lot more rough.
When Mike falls off of his motorbike, the stunt double used is obvious. Also, the area around him looks changed, or at least the angle.
When Mike straps on a knife, it causes a bulge around his ankle (despite his bell bottoms). In the following scenes, it's clear as he walks that the knife holster is gone.
As seen earlier, Reggie's ice cream truck has no roof over the cab. With the truck laying on its side, why would Mike have to climb up the undercarriage to the door to look inside the cab? He could have walked up to the right side and looked straight in the roofless side.
When Mike watches Jody and the girl in the cemetery, there is no way he could see her breasts, given the distance he is shown watching from and pose the couple was in, completely blocking his view of the girl.
When walking through Morningside Cemetery, after strapping on the knife, (at~31:45) the tombstones cast shadows to the left. Mike's shadow is cast to the right.
When Mike walks on the marble floor of the mausoleum, it sounds like he's wearing '70s large heeled shoes like the suited Jody in an earlier scene. Shots show he is in fact wearing flat-soled sneakers.
When The Tall Man breaks down the door of Mike's house, at the bottom of the door, a crew person's feet are visible running and pushing the door.
(at around 3 mins) At the beginning of the movie when Mike is joyriding on his motorcycle through the cemetery, the tracks of the trailer towing the motorcycle are visible in the grass behind him.
(at around 38 mins) You can see the stick making the finger move when it's in the box.
(at around 1h 11 mins) After Reggie makes the physical connection between the two nodes on the gateway, he falls backward onto the floor. In the letterbox edition, the ropes used to pull him back toward the gateway are briefly visible as he falls.
(at around 46 mins) In the car chase, Mike shouts that there is no one driving the car behind them; however, some poor lighting reveals a tall man driving the car.
Despite the brothers having some evidence and the eyewitness account of their friend Reggie, they still never contact the police? Jody had even mentioned that they were on their way to tell the police, but instead decides not to?
When Mike demands to be taken home, Sally doesn't even ask questions. When he orders her around, she neither complains nor asks questions despite her being an adult and Mike being a child.
(at around 42 mins) As Jody is putting his Colt M1911A1 pistol in his pocket in preparation for the final showdown at the morgue, he tells Mike that the gun is an official Army Colt. However, the pistol is chrome plated; handguns with this finish were never issued by the Army.