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The Shell Earrings are an item belonging to the the waitress on the Excess Express in Paper Mario: The Thousand-Year Door. During the events of Chapter 6, while Mario and his team were riding the Excess Express to Poshley Heights in search of the Garnet Star, they were stolen by the Shadow Sirens. Beldam, Marilyn and Doopliss (disguised as Zip Toad during the trip) needed the earrings to create an explosive form of Nitro Honey Syrup to bomb the train to prevent Team Mario from obtaining the Star; with this item being a source of seashell calcium, the other two items they needed were the Nitro Honey Syrup plans from the Businessman's briefcase and a source of gold (Toodles' Gold Ring). Thanks to Pennington and Team Mario, the evil trio's plan failed and all three stolen items were returned to their rightful owners. If Mario gives the Shell Earrings back to the Toad, she gives him a Star Piece.
According to in-game descriptions and the waitress herself, her ex-boyfriend gave her the Shell Earrings, who apparently talked to her via telephone shortly after Mario returned her earrings. Mario may have actually met this ex-boyfriend, because talking to a certain unnamed Squeek (who often tells Mario of his many love relationships) after beating Chapter 6 reveals that he was once in love with the waitress. Squeek also wonders if the waitress still cherishes them as he spoke to Mario.
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