Joe Camber's dog, Cujo, is infected with rabies from a bat bite. Cujo is a huge St. Bernard. Yeah, bad stuff very quickly starts to happen. Written in 1981 by Stephen King, and adapted into a film starring Dee Wallace in 1983.
This book/film contains examples of:
Adult Fear: Being trapped along with your sick child as a rabid dog waits for you just outside.
The Alleged Car: Donna's Ford Pinto. In fact, the whole reason why Donna and Tad are trapped is because they took it to Joe's to get the broken alternator fixed. By the time Cujo dies, it's in even worse shape.
Angry Guard Dog: Subverted with Cujo: he attacks people because of rabies, not because he was bred that way.
Big Friendly Dog: Cujo was one, before he got rabies. The Nightmare Fuel comes from how quickly a Big Friendly Dog is turned into a killing machine by the virus. There's a reason why most places require all registered dogs to get the rabies vaccine.
This extended to Real Life: a genuine problem in the making of the film because they simply could not get the St. Bernard playing him to act aggressively. They had to replace him with a cunningly disguised Rottweiler for several crucial scenes, and tape his tail to his leg so he didn't wag it constantly. Awww.
Catch Phrase: An in-story example. Vic Trenton, who works in advertising, along with his partner, Roger, creates a character called "The Sharp Cereal Professor", who becomes hugely popular. His catchphrase is "Nope, nothing wrong here".
Cuckold: Vic Trenton. His wife has an affair with Steve Kemp, and after she breaks it off, Kemp sends a crude message to Vic in revenge about how he enjoyed "fucking the shit out of her". He also mentions the mole Donna has on an intimate place, so Vic knows that the message is true. It causes him horrible emotional pain.
Domestic Abuser: Joe Camber. To the point (in the book) that during sex, his wife is afraid of crying out, because she's not sure he knows about female orgasms and it might upset him.
Eye Scream: Donna kills Cujo by thrusting the broken handle of a baseball bat through his eye socket.
Jerk with a Heart of Gold: Gary Pervier, in the book at least, has a touch of this. Despite being a full-blown grouch, to put it mildly, he's friends with Joe Camber, and doesn't mind Camber's son, either, but he has a genuine soft spot for Cujo (pre-rabies, of course) and even keeps some dog biscuits on hand for when the dog comes by.
Mama Bear: Donna's primal rage at the end is partly due to Cujo threatening her son, and partly due to early symptoms of rabies.
My Car Hates Me: Donna and Tad are trapped on the Cambers' farm, because her car (a Ford Pinto) wouldn't start (actually she went there to get it fixed).
Offscreen Moment of Awesome: Joe's death is only implied. As the most unlikeable character in the film, his death would have made for more satisfying viewing than the innocents Cujo savages.
Police Are Useless: Sheriff Bannerman lasts about 30 seconds with Cujo, and he is by far the most effective cop in the book.
Shell-Shocked Veteran: Gary Pervier. He served in World War II, where he had single-handedly taken a German pillbox, and was hit by six bullets. After that, he became an alcoholic and developed a nihilistic outlook on life (as he puts it, he doesn't give a shit about anything).
Tragic Villain: Cujo. He's shown to suffer terribly from rabies, and he attacks people because he believes that they are responsible for his pain. At the end of the book, it's written: "It would perhaps not be amiss to point out that he had always tried to be a good dog. [...] He had never wanted to kill anybody. He had been struck by something, possibly destiny, or fate, or only a degenerative nerve disease called rabies. Free will was not a factor."
Unwitting Instigator of Doom: That helpful mailman who points Vic Trenton in the direction of Joe Camber? If he had just minded his own business, Donna and her son wouldn't have had to experience the nightmare they went through.
Your Cheating Heart: Donna has had an affair with Steve Kemp and broke it off. This comes back to haunt her when a rejected Kemp vandalizes the house and wipes off a very important message on the blackboard that delayed her and Tad being found — contributing to Tad's death in the book.