Whale in Tree Hole

Doudou the Woodpecker is a forest doctor. He was very good at "beating drums to drive away insects" and cured many trees suffering from insect infestations. One day, Doudou, who was working in Baiyun Forest, discovered a strange thousand-year-old redwood. This redwood tree can be up to a thousand years old. It is not an exaggeration to call it the ancestor tree. Now, the tree ancestor made a mysterious sound. What will the woodpecker find when he goes around? Intention: Listen quietly