The Seithr plant grew on a small island in the northern seas. The oil of the plant, taken from the petals was harmless and used in the preservation of pearls, but when a certain incantation was spoken over it and a blood sacrifice was made it became a caustic poison. Ships such as the Waverunner made the perilous journey to fetch the plant. The oil which it made was prohibitively expensive. The oil from this plant was used in interrogations by the Razac.