Early drafts of the film's script, including the pressbook release, it stated that the werewolf speaks. In the actual film itself, the werewolf does not speak at anytime.
Producer Dino De Laurentiis was very unhappy with the werewolf used in the film. He was disappointed in both the way it looked and the way the costumed actor moved. This proved to be a bit of an insult to the actor wearing the suit as he was an accomplished modern dancer and was hired specifically for his movement skills.
According director Daniel Attias, Gary Busey ad libbed a great deal, for instance when Uncle Red is in the gun shop. Attias checked it with Stephen King, who said OK for it to be included.