Four-Flavored Wood

There is an immortal tree in the Qilian Mountains, called the four-flavored tree. It is actually like a jujube. When cut with a bamboo knife, it is sweet, with an iron knife it is bitter, when cut with a wooden knife it is sour, and when cut with a reed knife it is pungent. There are really no four flavors. The bitterness, sweetness and bitterness are all in the human heart.