After several days, the egg hatched and the little eagle came into the world.
Don't count your chicken before they are hatched.
Don't count your chickens before they're hatched!
Instead of passing out of the hen's body and being incubated outside, the egg was incubated in the hen for 21 days and then hatched inside the hen.
Chicken (1) Don't count your chickens before they're hatched.