A genre of expansionism, blueberry expansion is a fantasy fetish in which a female (and less commonly a male) turns blue, fills up with blueberry juice until they become spherical, and basically transforms into a human blueberry.
Blueberry fetishism draws its roots from the 1971 film Willy Wonka & the Chocolate Factory, where the character Violet Beauregarde transforms into a giant blueberry after chewing a fantastical piece of gum which contains a full three-course meal - the problem being in the dessert, with the blueberry pie.