Eggs are among the most nutritious and versatile ingredients we can find. After all, they're the energy packed payload for a fetus. However, they're also incredibly perishable. The ancient Chinese have developed at least a couple of methods of preserving eggs before the advent of refrigeration.
One method is through salting. Duck eggs are significantly richer than chicken eggs, and when they are brined, they become another entity altogether. Boiled and salted duck eggs are a unique ingredient; the yolk is intensely rich and seasoned, used often as the "treasure" in mooncakes and other treats. The best ones are said to ooze orange oil when cut. The whites are intensely salty, and probably compare with feta cheese.
Another way of preservation are the so-called "century" or "millenium" eggs - pidan -, prepared by wrapping eggs in alkaline clay for extended periods of time. The eggs transform dramatically, the whites turning in to a transparent brown jelly, and the yolks into creamy greenish gray, smelling faintly of ammonia and sulfur. Stuff is delicious cooked into congee, and there's a place in town that batters and deep fries them.
I've see pidan offered on "Fear Factor". How wimpish can you get? Jeez, I'll have two.