First of all chickens don't fight. It is cock fight (hen male). Not only in China, it is very common in India also. In this game of cock fight, it is the claws which is used by cock to hit the other cock. The fight goes on till one dies. In this attacking game, usually the beaks and nails are used as weapons. 'Carved out of stone' means that these weapons are so sharp and strong that they are made out of stone. Naturally in those period metals are more rare. Stone age story and these cock fights were prevalent then also.
Now teachers please comment.