Huey, Dewey, and Louie
During their stay in the valley, which the professor has named "Plain Awful", Huey, Dewey, and Louie blow some bubble gum bubbles, which is against the law in Plain Awful: It's forbidden to produce any round objects in the valley. The only way to get out of the valley and avoid capital punishment is for Huey, Dewey, and Louie to produce square bubbles. They manage to do that by teaching the square chickens to chew gum and blow bubbles. The nephews hid the chickens under their shirts and pretend they made the bubbles themselves.