Shell Earrings
The Shell Earrings are an item belonging to the the Toad Waitress on the Excess Express in Paper Mario: The Thousand-Year Door. Doopliss (disguised as Zip Toad at the time) stole the Waitress's Shell Earrings during Chapter 6 of Paper Mario: The Thousand-Year Door. The Shell Earrings were meant to be a part of the Shadow Sirens' plans to create an explosive form of Nitro Honey Syrup. To do so, they needed the Nitro Honey Syrup plans from the Businessman's briefcase, a source of gold (Toodles's Gold Ring was what they chose), and a source of seashell calcium. However, Mario puts an end to their plans, retrieving the lost items. If Mario gives the Shell Earrings back to the Toad, she gives him a Star Piece.
According to in-game descriptions and the Toad 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 Toad Waitress. Squeek also wonders if the waitress still cherishes them as he spoke to Mario.