easy for the writers in the first episode, but like Marge's warnings, they eventually got more difficult to write, so they were abandoned. Another reason they were dropped was that the tombstones would list television shows that had been canceled the previous season; after a few years, several of the shows that were canceled were produced by former Simpsons writers. However, after two decades, this gag made a brief comeback in "Treehouse of Horror XXIX" at the very beginning, this time appearing before the main opening sequence and title. While the early Treehouse of Horror episodes featured a Halloween themed opening sequence, the later ones only included the title and the "created by" and "developed by" credits. Every episode between "Treehouse of Horror III" and "Treehouse of Horror X" featured a couch gag with a Halloween theme, including the Simpson family dressed as skeletons, zombies, and characters from previous Halloween episodes. Wraparounds The first four Treehouse of Horror episodes had brief wraparounds that occurred before each segment and loosely tied together all three stories. "Treehouse of Horror" was the only one that actually included a treehouse as a setting. In that episode, Bart and Lisa sat in it telling stories to each other. "Treehouse of Horror II" presented all of the segments as being nightmares of Lisa, Bart and Homer; "Treehouse of Horror III" had Lisa, Bart and Grampa telling stories at a Halloween party; and "Treehouse of Horror IV" is presented by Bart in a parody of Rod Serling's Night Gallery. After a few years, the amount of broadcast time for an episode was shortened, allowing less time to tell a proper story. There were no wraparounds for "Treehouse of Horror V" because they had been cut to make more time for the segments. Following that, the writers permanently dropped them. Kang and Kodos Two characters that are virtually exclusive to the Treehouse of Horror series are Kang and Kodos, a pair of large green space aliens who were introduced in the "Hungry are the Damned" segment of "Treehouse of Horror". Kang and Kodos have since appeared in every Treehouse of Horror episode, sometimes as important parts of a story, but often just for brief cameos. In some episodes, they only appear in the opening segment, but often they will make a cameo appearance in the middle of a different story. For example, a story about zombies attacking the