Lean and muscular, with missing teeth and ears that "looked black with dirt", Xing taught Wu how to fight for survival in the camps. He showed Wu how to dig for underground rat burrows in order to find clean caches of grain and beans which could then later be boiled for food to avoid starvation. He also taught Wu how to be aggressive to discourage bullies. Wu came from an urban, educated background and was naive. Xing often repeated to Wu, "Nobody here will take care of you. You have to take care of yourself." Wu later wrote: