In Cujo, how is it that the St. Bernard becomes infected with rabies?

In Cujo, the St. Bernard becomes infected with rabies after sticking his nose into a rabbit hole and being bitten by a rabid bat.

Cujo is initially portrayed as a gentle, loyal family dog belonging to the Camber family. While chasing a rabbit near the Cambers’ property, he follows it into a hidden underground cave or burrow. The cave is inhabited by bats, including one carrying rabies, and the bat bites Cujo on the nose. The wound is small and initially goes unnoticed.

As the infection develops, Cujo’s behavior changes dramatically. Rabies causes confusion, aggression, fever, and neurological deterioration, transforming the previously friendly dog into the dangerous animal at the center of Stephen King’s 1981 horror novel. The disease—not a supernatural possession or deliberate evil—is the immediate explanation for his violence.

A common mix-up is remembering only that Cujo was bitten by a bat, without the rabbit chase and underground cave setting. The story’s 1983 film adaptation uses the same origin. The cave itself is never successfully located afterward, reinforcing the novel’s unsettling sense that the disaster began with an ordinary dog following instinct into an unknown place.