The dogs featured in the film would often have their tails tied down to their legs because the animals would be visibly enjoying themselves so much that they would wag their tails during filming. This tactic was missed once in the editing, where one shot clearly shows Cujo from behind, growling and supposedly ready to attack, but wagging his tail energetically. Such is also the case about 54 mins. in, after "Cujo" has finished his first kill: the dog must have broken out of its tail restraint, as it's wagging it unusually low, yet happily.
To make the St. Bernards attack the car, animal trainers put the dog's favorite toys inside the car so the dogs would try to get them.
Five St. Bernards were used, one mechanical head and a man in a dog costume.
Danny Pintauro actually bit Dee Wallace's fingers during his seizure scenes. Dee's reactions in the scene were quite real.
The foam around Cujo's mouth was made of a concoction of egg whites and sugar. The dogs caused problems on the set by constantly licking off the tasty mixture.