Hexagram H18 is named 蠱 (gǔ), Correcting. Other variations include work on what has been spoiled (decay), decaying and branch.[1] Its inner (lower) trigram is ☴ (巽 xùn) ground = (風) wind, and its outer (upper) trigram is ☶ (艮 gèn) bound = (山) mountain. Gu is the name of a venom-based poison traditionally used in Chinese witchcraft.