|Drawing of a Fei Gou, from 'Wu Bei Zhi (《武備志》)'.|
Fei Gou is used by siege defenders stationed on top of the city wall to hook at the legs of besieging troops (as lower legs are seldom armoured, plus besieging troops tend to keep their heads low to avoid incoming arrows, so they will not notice the relatively large Fei Gou). The defenders then pull the unfortunate victim to the top of the wall before releasing him and let him fall to his death (similar to how a sparrowhawk snatches its prey, which is probably where this weapon gets its name from). Even if the victim manages to dislodge the hook before he is pulled up, he will be unable to proceed with the siege due to leg injury.
To prevent the enemy from cutting off the rope, as well as to prevent the sharpened hook from severing its own rope, first portion of the rope is replaced by an iron chain.