In that year, the dog was outside when Cheryl Cunningham broke out into the open air from a small, squarish tunnel leading from the compound's main building. The two-headed dog fiercely barked at her, while running towards her, and then jumped at her, snarling ferociously.
Shortly thereafter, the dog bounded toward former FBI Special Agent Fox Mulder, instantly after he jumped over a tall chain-link fence surrounding the compound and began to intrude on the area. The two-headed beast growled and barked as it ran and leaped at Mulder, knocking him over. The noise of the commotion influenced the dog's owner, Janke Dacyshyn, to exit the main building but he heard the animal whimpering soon after he did so. The dog was lying on the snow-covered ground, with one of its heads bloodily bashed in and the other head whining sorrowfully. It barked squeakily when Dacyshyn approached the fallen beast, moments after the dog had been attacked by Mulder. (The X-Files: I Want to Believe)
In reality, the dog that played this role was named "Okie", so the crew nicknamed the other head "Dokey"; the latter head was an appliance that was attached to the actual dog by velcro. Okie, a male Rottweiler, was required to ferociously growl on cue from his handler, Paul Jasper, and did so without any problems.
20th Century Fox was extremely concerned about the concept of a two-headed dog, as such an unnatural being could look silly very easily, so director Chris Carter was very careful to film the animal obliquely – with the second head back-lit and silhouetted – so that the audience did not see the fake head too well and were not too sure of what they were seeing. In the filming of the scene wherein the two-headed dog attacks Mulder, however, Chris Carter imagined that the beast would be much more obscured than it ultimately was and thought the final version of the scene would show less gnashing of dogs' teeth than it does, although he was thankful to the film's editorial team for making the changes.
During production, Carter did preempt, as did other members of the crew, that they would have some trouble with the MPAA over the scene in which the injured dog is shown and that both the extremity of the scene and, in particular, how much blood could be shown would become controversial. When the wounded dog is shown lying down, steam was added to the shot, coming out of the mouth of the injured second head.