The IOU is an item found in Freddi Fish 4: The Case of the Hogfish Rustlers of Briny Gulch. It is seen being dropped by Gill Barker as he was introducing himself to Freddi and Luther. When Freddi reads it, she wonder what it was. But Gill immediately snatches it away from her and fibs by telling them it is just a poem. He then eats his IOU. It is one of the clues to see if Gill is Mr. Big and the mastermind behind the rustling.