Corrected entry: After Cujo kills his owner, the friend comes to check on him. After finding the owner, the guy picks up the phone, the dog attacks, and the phone falls, off the hook, and isn't replaced. Later the phone rings, but with those kind of phones, if one was off the hook the whole house would be off the hook, so no incoming call could be received.
Corrected entry: When Cujo attacks a cop in the hallway of the house, you can see the dog's tail wagging madly. Actually, the tip of the tail, since the rest of the tail has so obviously been strapped to one of its legs.