The above child song is sang during a game where a kid acts as ghost, blind folded and squats in the centre of a circle of children. The children would start singing the above song and when the song halted. If the ‘ghost’ had guessed who is behind ‘it’, then the said child shall become the ‘ghost’. In another words, this child song is implicitly indicating “the ghost at the back at that instance, shall replace the bird in the cage (to suffer). The Chinese call it 替死鬼 or simply ‘replacement ghost’.
So next time when you are passing through a garden, please be very careful of birds on the tree branch… for are they laughing at you because you may just carrying a extremely fair and horrible Japanese doll which incidentally can cry and call out loud for her mom!