鹬蚌持争，渔翁得利

Explanation: Metaphor of the two sides at loggerheads over, will suffer, so that a third party an advantage. 　　Source: "Warring Yan policy II," recorded in the clam shell open sun, sandpipers to peck at it, the mouth is clamped clam shells, the two areas are not to give way. Fisherman came, the two are caught.