《天工开物·上篇·乃服》
小竹竿的一头垂下一个小石块为活头。当连接断丝时，一拉小绳，小钩就落下来了。
小竹坠石为活头，接断之时，扳之即下。
A small stone is hung at one end of the small bamboo pole as a movable head. When connecting broken threads, the small hook will fall off when pulling the small rope.