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A trip to the Springfield Family Fun Center proves to be a lucky one for successful bully Nelson Muntz (voice of Nancy Cartwright) when he wins a brand new BB gun, and Bart Simpson (also voiced by Cartwright), suitably impressed, asks if he can come over some time and try it out. Bart's mother Marge (voice of Julie Kavner) is aware of Nelson's thuggish tendencies and doesn't care for guns, so she forbids Bart to spend time with Nelson. Bart stops by his house after school anyway, and while trying out the gun accidentally kills a bird. Marge arrives just in time to see Bart in action, and rather than yell at her boy, she tells him she's given up on him. Bart senses he's finally crossed a dangerous line, and when he sees several unhatched eggs in the late bird's nest, he takes the back to his tree house in order to hatch them. While Bart tries to keep the egg-hatching project a secret, when Marge finds out it gives her a new faith in her son. However, when the eggs finally hatch, to the surprise of everyone what emerges aren't birds but Bolivian Tree Lizards, which have been declared a menace to wildlife by the U.S. Wildlife Department. "Bart The Mother" featured a voice cameo from Phil Hartman as Troy McClure in what proved to be his final appearance on the show; the episode first aired on September 27, 1998.