I saw the eye spots and black body of this caterpillar in the weeds and thought it was a snake! Sneaking up closer to get a picture, I realized that it was an enormous caterpillar (about 12cm long), but I had no idea what butterfly/moth it would turn into. Eventually I found out on Internet that it’s the larva of an Impatiens Hawk Moth or sesujisuzume.
Impatiens Hawk Moth = sesujisuzume = Theretra oldenlandiae
Information (and pictures of adult moth): http://tpittaway.tripod.com/china/t_old.htm