Hexagram 18 is named 蠱 (gǔ), “Correcting”. Other variations include “work on what has been spoiled (decay)”, decaying and “branch”.Its inner trigram is ☴ (巽 xùn) ground = (風) wind, and its outer trigram is ☶ (艮 gèn) bound = (山) mountain. Gu is the name of a venom-based poison traditionally used in Chinese witchcraft.