Also known as fern cake, the book is called fern powder. The raw material is wild ferns growing in Ershan Mountain at an altitude of 1200m. Digging ferns is called "opening the ground warehouse", which means the grain stored underground by God for the common people. It has been a life-saving grain for Tujia people to survive the famine since ancient times. From the first year to the famine, it is difficult for people to fight ferns in droves. When a crow climbs a mountain, it will dig a hole one meter deep to get fern roots. After the fern root is washed, it is beaten into velvet shape with wooden vertebrae and then precipitated into powder. Starch is made into a ball, dark gray in color, and it is a root stalk. Dig fern root 100 kg every day, and make it the next day. Those who dig fern roots in distant mountains often sleep in wild mountains, keep company with wolves and eat root mud.