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Bart met Goose while trying to find a distributor for his T-shirts at the Springfield Novelty Expo. When Bart got frustrated and walked out of the expo, Goose accidentally ran into Bart with his car, scattering T-shirts everywhere. As Goose helped to gather up Bart's shirts, he was impressed with the slogans and offered to sell them in his stores. The shirts proved to be a hot seller and became nationally known, making plenty of money for both Goose and Bart.
Goose later sold the T-shirt line to Disney and used some clever legal maneuvering to keep Bart from getting any money from the sale. However, when Homer threatened him with a home-made miniature nuclear reactor, Goose relented and gave Bart a large (but unspecified) amount of cash.
Eccentric demeanor notwithstanding, Goose is cleverer than he lets on. He seems to be skilled at breaking and entering, illusion, and gadgetry in general. When Goose visits the Simpson home, he manages to sneak into the house when they're all at the front answering the door. He also produces confetti and flowers (which he gives to Marge) from out of his hat, leaves from out of nowhere, and roller skates from out of the bottoms of his shoes. Another one of Goose's tricks is disappearing in his own shop (albeit not always successfully), thanks to a hidden trapdoor.
Goose also has enough business sense to manage a successful chain of joke shops (which he tongue-in-cheekily refers to as "over 20 stores in over 30 states") and to retain lawyers to avoid paying Bart any of the proceeds from the sale of his T-shirt line.
 Behind the Laughter