A thirteenth-century Song dynasty text about commerce describes dangers faced by pearl divers, who sometimes fell prey to “huge fishes, dragons, and other sea monsters” that would rip open their stomachs or bite off their feet. A pearl was considered most valuable if perfectly round; the test was “that it will not cease rolling about all day when put on a plate.” To avoid heavy export duties, foreign traders sometimes concealed pearls in canes or umbrella handles.