鹬蚌相争

A clam（蛤） swam to the bank and opened its shell in the sun. A snipe flew over and saw a piece of red meat on the ground, so it dived to the ground and pecked at the clam. Before the snipe drew back its beak, it was gripped tightly inside because the clam suddenly felt a sharp pain and closed its shell quickly. The snipe shook its head violently to cast off（躲开，抛弃） the clam, but it failed no matter how hard it tried. 

The snipe said angrily, "Listen, you clam, it's not going to rain today, neither will it tomorrow. Then you'll die from thirst. So quick! Let me off!"

The clam was angry too. "You listen, I won't let you off today, and I won't let you off tomorrow, either. Then you'll die of hunger. Do you still dare to eat me?"

The snipe and clam were locked in fight and quarreled, and neither of them liked to give in first. Just at that moment, an old fisherman came. He picked them up and took them home for dinner.

The story tells us that the third party will have an advantage fall into his lap when the other two parties are locked in combat for their own personal interests.