吃里爬外 is formed by combining the verb 吃 (eat) with the location 里 (inside) and the verb 爬 (crawl) with the location 外 (outside), creating a literal sequence of "eating inside and crawling outside". This structure juxtaposes two opposing spatial actions to metaphorically depict the act of consuming resources from one's own group while covertly assisting external parties, thus conveying betrayal through direct contrast between internal benefit and external allegiance.