I know the topic sounds straight forward. But I want to understand how a hen can start a clutch of eggs and not be present on the nest all day letting the eggs cool. She lays the first egg and later begins siting on all the eggs for 21 days laying 1 more egg each day. How is it possible that they all hatch at the same time when laid on different days? I know chickens are magical but I want to understand this magic. Thanks.