A goose's reproductive anatomy is quite unique compared to most birds. Unlike many avian species that have simple reproductive structures, male geese possess a phallus, which is unusual for birds. The goose's phallus is long, corkscrew-shaped, and retractable, meaning it can extend during mating and withdraw when not in use. This structure evolved to facilitate reproduction in water environments, where many waterfowl, including geese, live. The corkscrew shape allows for successful fertilization despite the challenges posed by their aquatic lifestyle.