You will know after you try it twice. I have lived in Nanjing for more than two years and now I am in Shanghai. I feel like the Laoya Vermicelli Soup in Shanghai is rubbish. The duck blood vermicelli soup in Nanjing tastes better, and the duck blood, duck liver and duck intestines do not have the chewy gizzards. Just like after leaving Lanzhou, it is difficult to find authentic Lanzhou ramen, although there are many ramen shops in the street.