offensive, Parker specifically defended the episodes "Mr. Hankey, the Christmas Poo" and "Big Gay Al's Big Gay Boat Ride", which he felt included moral values and a "sweet side to it" among the sophomoric humor. Stone also said those two episodes became the specific shows people would most talk about when they discussed South Park. Animation Actor George Clooney provided the small role of the voice of Sparky, which is limited entirely to dog barks. Clooney was a vocal South Park fan and was largely responsible for generating news about "The Spirit of Christmas", a 1995 animated short film by Parker and Stone that served as a precursor to South Park. Parker said they decided to cast a famous actor in the small role of Sparky because "we thought it was funny", and because they wanted to do something different from the animated series The Simpsons, which is known for having prominent guest appearances on a regular basis. Parker added, "Since South Park is sort of a show that rips on celebrity, we wanted to degrade them in other ways too. And we thought let's have celebrities on, but have them do really minor, unimportant things". Comedy Central executives were excited at the prospect of having Clooney appear on the show, but Parker said they were disappointed to learn his role was so small. South Park animators created the episode using PowerAnimator, the Alias Systems Corporation animation program most commonly known as "Alias". It was particularly challenging for animators to design the complex scheme of lights during the episode's disco club scene. Eric Stough, director of animation for the series, said it took one of the technical directors "about half a day" to set up the brief scene. Parker said he was particularly happy with the animation in "Big Gay Al's Big Gay Boat Ride", and said he believed the series was starting to settle into the defined look it has retained throughout the years. Parker said, "I think that this was where we finally felt like we got it right, we got the look of it right". However, the animation includes some perspective errors, particularly during the football scenes, where Chef stands about as wide as a 10-yard marking on the field. Parker said the animators worked for a long time on the snow in the outdoor scenes, but ultimately decided they did not like how it came out.