Continuity mistake: In an overhead shot of the family picnic, there is a metal box on a ground-cloth that is in front of the wicker basket. When it cuts, the metal box is on the left side of the wicker basket.
Continuity mistake: When Ellie sits on the couch and asks "Is Missy in heaven?" the distance between her and Louis changes between shots.
Continuity mistake: In the scene where the father is in Jud Crandall's house looking for Gage, he is upstairs in the bedroom kneeling beside the bed holding a syringe. After he sees Jud dead, he gasps and you see him bite his fist with his right hand (the hand which was previously holding the syringe). Then the camera cuts back and he is again holding the syringe in his hand.
Continuity mistake: After Ellie turns off the TV, Church turns around to look at her twice.
Continuity mistake: When the neighbours' house is burned down near the end of the film, it is shown briefly three more times without any damage.
Continuity mistake: When Victor's corpse is in the hospital, the position of the streaks of blood down the middle of his forehead next to the wound change between shots.
Continuity mistake: In the scene at the table where Jud admits he is to blame for what happened to Gage, Louis is talking to him and the scene cuts to a wide shot. As Louis is talking he is looking at Jud and has his mouth open. Cut, and his head is down and his mouth closed.
Continuity mistake: When Louis enters his garage, he leans his rake against the wall. When Church the cat runs out, the angle of the rake is different.
Other mistake: In the beginning of the scene where Gage is killed by the Orinco truck, the truck leaves the plant. The number on the trailer is marked T-80. In the scene, the truck rolls over in the accident. In later scenes where Rachel hitches a ride home with another Orinco truck, the number on the trailer is also marked T-80.
Continuity mistake: When Ellie runs to the tire-swing, she does a cartwheel and looses her hat, but in the next shot, her hat's back on her head.
Answer: Because in the book, the sign at the entrance to the "Pet Semetary" was written by some anonymous child. Clearly he/she couldn't spell that well yet.
Grumpy Scot