The Giant Worm is a two-headed, worm-like monster that dwelled by the seashore. A conjoined twin, one brother speaks with a high-pitched voice (Tim Curry), while the other brother speaks with a deep-pitched voice (Phil LaMarr). According to legend, the Worm is a magical creature that can grant any wish.
Jack traveled to meet the creature so he could wish to return home; but the Worm demanded that Jack answer a few questions to determine which one of the two heads really had the magic powers. If he guessed right, he would be eaten and taken to a "magical place" where all his desires would come true; if he guessed wrong, he would be eaten and digested for "500 years".
First, the Worms had Jack go through a "knock-knock joke" routine. Second, they asked him what his favorite color was. And last, they asked Jack to figure out which one of them was the real Magic Worm; they added that one of them only tells the truth, while the other one only tells lies. When Jack believed that he had solved the riddle and pointed at one of the heads, he was swallowed whole. But then the two brothers admitted to each other that they're both liars. Jack soon realizes that the Worm was not magical, as he sits among a bunch of malnourished old men in rags, who were also devoured by the monster, waiting to be freed.
How Jack escaped from the belly of this beast is not shown, but he most likely cut through their stomach with his sword, which likely killed the monster.