The dogs featured in the film would often have their tails tied down to their legs because the dogs would be enjoying themselves so much that they would wag their tails during filming. This tactic was missed once in the editing where they show Cujo from behind ready to attack and his tail is wagging energetically.
Five St. Bernards were used, one mechanical head and a man in a dog costume.
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.
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.
Danny Pintauro actually bit Dee Wallace's fingers during his seizure scenes. Dee's reactions in the scene were quite real.