Moosel's imagination goes out of control when he accuses everything of being a monster or an omen, and believes a real and friendly monster is all in his head.
Moosel's wild imagination manages to get him into a lot of trouble while the Wuzzles are out picking appleberries. It finally gets so bad that a boulder manages to crash into the dam. When Moosel is sent home, he suddenly thinks that he is imagining a big monster that keeps following him around.
It is actually a real monster with a very bad toothache. When the other Wuzzles see it and convince Moosel that it is a real monster, it offers to help save the leaking dam.