(at around 5 mins) When Louis is checking on Ellie after she fell off the tire swing he is wearing a tee shirt without a collar and sleeves that are rolled up midway past his elbow. When Rachel gets up to rush after Gage his tee shirt is now an open shirt with stripes and a collar. In the next shot when he gets up to follow Rachel his shirt is once again back to a tee shirt.
When Louis is checking on Ellie after she fell off the tire swing in the next shot when the tire is visible again, the tire now has a rim on it.
In the beginning when the family asks about the trail to the woods it is shown as a bare footpath. In later day shots it becomes sparsely lined with dull river rocks, and at night it shows a denser line of different, reflective stones.
(at around 1h 25 mins) When Louis falls out of bed, he hits his head on a nightstand, dragging a pillow off the bed when he falls. The pillow is shown very clearly on the floor between the bed and the nightstand. A few shots later the pillow is back on the bed again.
(at around 4 mins) When the Creeds arrive to their home, Ellie runs towards the tree-swing and her hat falls off. In the next shot, she is still running and her hat is back on.
After Victor Pascow's death, Dr. Creed throws his patient file into the trash can. No patient's file should simply be thrown away, especially after the patient was involved in an accident which would require a full investigation (including the use of his medical records).
(at around 57 mins) When Bill Baterman is looking at his son Timmy's Purple Heart, the enclosed ribbon and lapel pin in the case are for a completely different medal. The ribbon should be identical to the cloth portion of the Purple Heart.
When they first arrive at their new house and Gage is next to the car's trunk you can see cat food in the bottom right corner of the screen used to get a reaction out of the cat.
In the outdoor scenes where Louis is alone on Thanksgiving weekend, the trees in the background have leaves on them. In Maine at Thanksgiving time, the trees would have been bare.
In the picnic scene preceding Gage's death, Rachel and Ellie are both wearing sleeveless and backless dresses, and Gage is wearing short sleeves, despite this scene taking place sometime after Thanksgiving in Maine.
At the end of the movie, when Gage's body is lit ablaze, it's clearly a doll and not a real body.
When the security car shines its spotlight at Gage's grave, it fully illuminates it, so there is no way that anyone inside the car could miss seeing Louis standing in the grave, or the mounds of dirt piled around it.
In the flashback when Jud's dog Spot comes back, Jud's mother says that the dog is coming out of the ground that Jud buried him in. However, this line is said whilst in their garden, whereas Jud would need to have buried Spot in the ground at the pet sematary for him to come back.
In the German version, Gage's voice sounds like a 7-year-old child, but his laugh sounds like a baby / 1-year-old.
After Rachel tells Louis about how she had found Zelda dead, Louis refers to Zelda as "clinically insane". The word "insane" has been discarded by clinicians as stigmatising for many decades, since well before the film was made. It is very unlikely that a doctor would use this term to describe Zelda, especially when trying to comfort Zelda's sister over her death.