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 his pant legs are down. When Rachel gets up to rush after Gage his pants legs are now rolled up. When he gets up to follow Rachel his pants legs are once again down.
When the family arrives at the beginning of the movie Ellie does a cartwheel in a wide shot. The cartwheel causes her hat to fly off. In the next tight shot she's completing the cartwheel and her hat is back on her head.
When the family first arrives and Gage walks to the back of the station wagon to see their cat Church, his bowl is on the right side of the carrier in front of him. In the next shot of Church in the carrier (immediately after they show Gage's face looking at him), the bowl is on the left side, behind the cat.
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.
Just before Gage gets hit by the Orinco gas truck, it is shown leaving the depot and driving on US Route 15. However, US Route 15 runs through the states of New York to the end in South Carolina. This film is set in the state of Maine.
Gage ran out in front of a tanker truck that was displaying a "Dangerous" placard. On a tanker the placard would be the type product being hauled (i.e. "Flammable", "Corrosive" etc). The "Dangerous placard is reserved for mixed hazardous materials. You don't mix on a tanker.
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 Jud is attacked by Gage with scalpel neither wound inflicted bleeds. You would expect there to be some blood on the scalpel when Gage is shown holding it between the heel and face slices given how deep the blade went into Jud's heel but it's spotless.
When Jud is first showing the Creeds the "Pet Sematary" Jud tells Ellie that his dog Spot died of old age. He later tells Louis that Spot died because he got caught in barbed wire and got infected. This is actually an important plot point. The dog died of gangrene, the young Jud resurrected him, and a few years later the dog died again of old age.