It is a duck egg that has been fertilized and allowed to age somewhere between 18 and 21 days—just long enough for the yolk to develop into an embryo resembling a primordial creature with beak, eyes, body and feathers. The eggs are boiled for 20 minutes and served in the shell with a little salt, lime juice, basil and eaten in the same way you would a ‘normal’ chicken egg.
The older it is, the larger the chick and the more pronounced its feathers, bones, and beak. An embryo at 17 days has beak and feathers which are more developed at 20 days. Normally, after being fertilized, a chick hatches after 26 to 28 days of incubation. The taste depends on the breed of duck.