About EditCujo is a regular dog for the first part of the movie, but a bite from a vicious bat turns the once friendly Saint Bernard into a terrible beast that kills anyone and everyone who is daring enough to cross paths with him. Donna Trenton and her son, Tad, are going to Cujo's owner's house when their car breaks down. To make things worse, Cujo, who had already claimed two victims in the house, is lurking just outside the car, ready to attack them. He attempts to kill Donna and Tad continuously while they are stuck in the car. Donna tries sevral times to repair the car, but Cujo attacks her. The two of them run into the house. While inside, Tad faints of thirst. Donna finds a baseball bat and hits the dog with it repeatedly. When the bat breaks, she stabs him with it. The dog drops, thought to be dead. Donna runs to the kitchen where the Cujo who was "playing dead", leaps through the window and attempts to kill her.
Nobody can stop this beast until Donna kills him by shooting him with the pistol that belonged to the Sheriff that Cujo killed earlier. Cujo appears to have survived however, as he makes a brief appearance in the film Cat's Eye where he is shown chasing the films titular cat.