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Rob's mother presents Laura (Mary Tyler Moore) with a Petrie family heirloom -- a hideous-looking brooch, in the shape of the United States, studded with diamonds. Legend has it that the brooch is cursed; every time a diamond falls out, a Petrie will die. This proves to be a great source of panic for Laura when she accidentally drops the brooch down the garbage disposal -- thereby figuratively wiping out the entire Petrie clan!