The egg song is a way to distract potential predators from the nest. It allows the chicken to get the predator's attention so the nest stays hidden and unharmed, the eggs can't protect themselves.I have always wondered what the "bok bok bok bok bok BAGERK" sound means - I have read that it can mean either laying or predators - but our chicken does it with neither of those cues. She will often do it when the other hen is laying an egg, almost as if to announce that the other hen is laying, but I would've thought that this wouldn't be a great strategy - announcing to possible predators that there is a hen all vulnerable on a nest!