A happy accident of pearl farming, keshi pearls are produced by chance. Saltwater oysters sometimes reject their bead implant, but particles of the accompanying mantle tissue remain and stimulate the production of nacre in flat, petal-like shapes. They are often removed as seed pearls, inspiring their name, meaning "poppy seed" in Japanese. While some people think they should be considered natural pearls, they are a by-product of the culturing process so this is not technically correct. One of the most striking characteristics of South Sea keshi pearls is their very intense luster and iridescence, sometimes greater than seen in the finest cultured pearls.