Story of these mans :
In 1010, King of Vietnam had a serious illness, his healer needed a Red Worm for King's medicine. Then, the King has ordered to two strongest and smartest mans to go to get Red Worm in a remote and craggy Black Mountain. They took Red Worm easily, but the way back is not favorable.
These man have to keep the Worm (type of high toxicity) crawling in a dish (If not, Red Worm could spins itself a silky cocoon and turn into a Butterfly). Because of that, Two man are not able to work at the same time . And sometime they couldn't do anything except holding the dish ( In that time, that man will turn their color to red ).