You have to be careful buying eggs round here. These make look like regular eggs to you.
but shell them to find these - 皮蛋 (pí dàn) aka century eggs, preserved eggs, hundred-year eggs, thousand-year eggs, thousand-year-old eggs, millennium eggs, skin eggs orblack eggs.
Here served with chilli sauce.
Delicious.
P.S. The easiest way to tell if they are pidan or fresh eggs (assuming you can't read the Chinese on the signs) is that fresh eggs are sold by weight, whereas these are sold by the unit. ¥1.50/个 (¥1.50 each ) or 22 cents US; 17 pence UK.