I am incubating 3 duck eggs, 2 look normal and 1 looks like this. They are 21 days old, and all 3 are twitching and moving about gently. A strange clear gap has appeared on the side of the egg, next to the air pocket. It is moving gently and responds to the light when candled, but I don't think it's looking good. The egg looks perfectly normal, even thickness all over and has a good sized air pocket. Does anyone know what this means? Lack of development? Suffocation? Horribly disfigured? Still born? The gap itself, which should be covered with little veins, probably takes up about 1/4 of the egg.