I have had quite a few people who did not know the following:
Hens do not need a rooster to lay eggs. Without a rooster, they will lay infertile eggs. What you buy from a grocery store is infertile eggs. If there is a rooster, they will lay fertile eggs if he covers all of the hens every day. The rule of thumb is that a healthy rooster can cover about 10 hens. If he misses a hen on a particular day, she will lay an infertile egg a few days later. It takes a few days from when the egg is released from the chicken's ovaries to pass through her oviduct until the albumen (egg white), membrane, and shell is added. Then it is laid in the nest. In other words, there can be several eggs in different stages inside of the hen.
If you buy eggs from a farm that has a rooster in with the hens, you might see some evidence of development if the eggs were kept warm enough. Summertime temperatures can cause partial development. That's why it is best for the flock owner to pick the eggs up a few times a day and put them in the fridge or cool spot in the house. The cook who buys from a farmer or produces their own eggs should use a separate bowl to crack each egg before adding to the main mixing bowl.
It was one of those conversations that go around and around in circles. After many questions from two adults and one very curious child, I tried to spell it out without getting graphic. "Look, the chickens need to do the same thing we do to make a baby. Male and female need to get together. Their development occurs outside of the body in this little egg while ours occurs inside a womb. No seed = no chick...just an egg." Then they wanted to know if a lightbulb in a dresser would hatch the same eggs we were discussing. (Fly Away Home makes it look so simple!) I gave up trying to correct their thinking. I told them to try it, and see how it worked.
We still laugh about it!