Revealing mistake: When Louis goes to give Gage the shot, if you look closely, you can see that the needle is just a fake prop and doesn't leave a puncture mark.
Pet Sematary (1989)
Ending / spoiler
Directed by: Mary Lambert
Starring: Dale Midkiff, Denise Crosby, Fred Gwynne, Brad Greenquist
Gage kills Jud Crandall and his mother. Louis injects poison into Gage. Louis buries his wife in the pet cemetery, not listening to Victor Pascow's warning. Louis's wife comes back and they kiss. She knifes him...
Creed
More mistakes in Pet Sematary
Jud Crandall: How's your cat, Louis?
Louis Creed: It's Ellie's cat.
Jud Crandall: No. It's your cat now.
Trivia: At the beginning of the movie when it shows the pet graves in the Pet Sematary there is a grave that says, "Smucky the Cat, he was obedient." Smucky the Cat was actually Stephen King's daughter's cat that was killed.
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