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.
Revealing mistake: When Louis sets Gage's lifeless body on fire, it becomes apparent that it is a stunt dummy. The body resembles a small, pale mannequin with vague facial features and a wig.
Continuity mistake: When Ellie falls off the tire swing at the beginning of the film, the tire shown in the first shot of her on the ground is not the same one that was tied to the tree. It is a whitewall tire with brand new tread, and the rope is nowhere to be seen in this shot. A moment later when her parents run over, the older worn-down tire with the rope tied around it reappears. (00:05:10)
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.
Revealing mistake: When the mother gets into an accident after her tire blows, the ghost shows up. It is floating above her car. Notice the seam where the ghost is on the car. When the scene shakes slightly, the ghost shakes too indicating it was a poorly superimposed shot.
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: 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.
Visible crew/equipment: After Louis makes the promise to Ellie by telling her, "Church will be fine," Louis heads out the door and down the stairs. The reflection of the boom pole/mic is visible on the red vehicle's windows, just as Missy drives past Louis. (00:16:00)
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