A simile is a literary technique that uses the words "like" or "as" to compare two unrelated things. In this passage, Hueitse is comparing Chuangtse's words to a gnarled, knotty tree. Like the tree, he is saying that Chuangtse's words are "big and useless." When looking for similes, look for the words "like" or "as." Hueitse says, "Your words are LIKE that tree."