Lisa escapes, but Bart activates the "Super Fun Happy Slide", causing him to slide back down into the vampire pit, whereupon he is captured and bitten by Mr. Burns. Lisa tries to warn her parents, but Burns reappears with Bart who is now very pale and is behaving oddly. But these factors get little attention by the family. Later that night, Lisa is awakened by a now undead Bart and his vampire friends. When Bart is about to bite Lisa, Homer and Marge interrupt and discover that Bart is a vampire. Lisa claims that the only way to restore him is to kill the head vampire, Mr. Burns. The family returns to Mr. Burns' mansion, where Homer drives a stake through Mr. Burns' heart (after first hitting his crotch), causing him to dissolve into sand (but not before Mr. Burns tells Homer "You're Fired!"). The next morning, however, Lisa discovers that everyone else in the Simpson family is a vampire, with Marge as their head. The family closes in on Lisa, but instead of attacking, they break character and wish the home audience a happy Halloween. Then, they all harmonize "Hark the Herald Angels Sing", parodying "A Charlie Brown Christmas". "Treehouse of Horror IV" was directed by David Silverman and co-written by Conan O'Brien, Bill Oakley, Josh Weinstein, Greg Daniels, Dan McGrath, and Bill Canterbury. It is the fourth episode of the annual "Treehouse of Horror" Halloween specials. As with the rest of the Halloween specials, the episode is considered non-canon and falls outside the show's regular continuity. O'Brien worked on the "wraparounds" of Bart introducing each segment to make sure that they "pulled" the episode together. The wraparounds are based on Rod Serling's television series "Night Gallery", in which Serling appears at an art gallery and introduces each episode by unveiling paintings depicting the stories. Executive producer James L. Brooks loved the show, so it was "great fun" for him to do the parody. Show runner David Mirkin thought the "Treehouse of Horror" episodes were the hardest episodes to do because the staff had to fit in all three stories in only 22 minutes. Mirkin said, "Things had to happen really fast. They're really just crammed with jokes and story beats and everything." The first segment, "The Devil and Homer Simpson", was written by Daniels and McGrath. The first time Devil Flanders appears, he looks the same as the devil Chernabog from the 1940 Walt Disney produced film "Fantasia"; Silverman particularly admired the animation in that sequence.