Half-hatched eggs are basically fertilized duck eggs (a.k.a. fetal duck eggs) that are 16 to 20 days in age. 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. Hot vit lon from Muscovy ducks (a leading breed in the U.S.) are considered among the best. You can half-hatch chicken eggs too but duck eggs are larger and more prized.