Thousand- year old eggs, aka century eggs, are a Chinese delicacy that puzzle a lot of people. In Chinese, they are called Pei Dan, ie. ‘skin eggs’. They have a pretty coating of husk and ash on the outside. They look just like any other egg when the coating is removed. However, once cut, the pungent smell of ammonia distinguishes themselves from the others. (Some people believe that it was because the process was started by horse urine!) The ‘egg white’ is no longer ‘white’. It is a dark brown substance with the consistency of jelly. The ‘yolk’ is not orange nor yellow like normal eggs. It is dark grey with a hint of green. Who on earth would want to put them in the mouth?
I would because they are yummy and unique! Though I would rather not have them on their own, but with with pickled ginger(see photo above). The ginger is refreshing and it complements the eggs very well. This way of eating is popular as a snack before a meal, for example before hot-pot.
Another classic way of having thousand-year old eggs is to add them to congee, aka Chinese rice porridge, together with pork slices. The preserved egg yolks enhance the flavour of the congee and the egg ‘jelly’ makes the texture of the congee more interesting. A good thousand-year old egg should have only a weak smell of ammonia. It should have a full body and the egg ‘jelly’ inside should show the pattern of pine leaves . Good eggs are usually sold by street hawkers and local shops (not supermarkets!).
Winkypedia 
i like it
it is yummy! definitely worth trying.