Belly of the Beast is the 21st episode of Season 2 of Adventure Time. It first aired on April 4, 2011.
The episode starts with Finn and Jake lying in their beds, and the ground shaking. Finn asks what's shaking, and the guys see a monster outside. They interpret this as a dream, and go out to fight the monster. But when Jake gets hit away, they realize that it is not a dream, and then here someone's voice coming from inside the monster's stomach. The go inside the monster, and find a bear, who is screaming for help.