Folklore: I Have a Living Pen Pal

Xie Zhi grew up in a village and had a pen pal he had exchanged letters with for years; But lately, he had begun to suspect that his pen pal might actually be alive. His pen pal invited him to meet in person, and Xie Zhi was tempted. After all, the living should be with the living; His grandmother told him that if he carried a letter from a living person and kept walking east, he might be able to enter that world; The good news was, he made it; The bad news was, he seemed to have brought the village monster, Xiong Gapo, along with him! He had only meant to go out and broaden his horizons, but now he had no choice; He had to deal with Xiong Gapo! His grandmother had taught him that digging out the second vertebra from a monster's back gave him a chance to use some of its abilities; But can someone tell him why supernatural incidents are becoming more and more common here? Why does everyone here say he came from a "cage"? Oh, right. You want to know who Xie Zhi's grandmother is? Everyone calls her the Snake-Bone Granny;