The huatou method, various translated as "critical phrase," "source of the words," or "that which is before words," is unique to Chan Buddhism among the world's spiritual traditions. The huatou refers to the "punchline" of a gong'an (Jp: kōan), which students meditate on to cultivate a feeling of wonderment towards their mind and the world. When the wonderment reaches a fever pitch, the student may suddenly awaken.

Guo Gu explains the history and practice of this unique method, as well as its special characteristics. Notably, unlike many other methods in Buddhism, the huatou is best suited to use within everyday life, rather than when sitting still on the cushion.