《淮南子·人间训》
所以会出现上述的现象。魏国将领乐羊率部队攻打中山国。他的儿子被中山人抓起来扣押在城内。
魏将乐羊攻中山，其子执在城中。
Therefore, the above phenomenon occurs. Wei general Le Yang led his troops to attack the state of Zhongshan. His son was captured by the people of Zhongshan and held in the city.