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Limpets are a type of shell-fish. They are often considered by Vikings to be disgusting as food, often to the point that consumption of them is used as a type of punishment. In the book How to be a Pirate, Hiccup and the rest of the Hairy Hooligans visit the Isle of the Skullions where Skullions are trapped and forced to live on limpets. Gobber often used limpets to threaten the the Hooligan boys.