If a baby Fairy-Wren wants food, he has to give the password first.
He’ll know it off by heart—because he learned it before he was hatched, while he was still inside his egg.
The Superb Fairy-Wren (its scientific name is Malurus cyaneus) is an Australia bird.
It teaches its babies a single note, even before the baby is hatched.
The mother wren sings the note over and over to her unhatched eggs.
The mother teaches the note to the father wren so he can sing it to the eggs, too.