Melody.

An owl teaches his class full of birds about melody. It's all around in nature. Only birds and man can sing; man "sings" even when he speaks. We see a quick survey of the stages of life, as captured by songs: the alphabet song for primary school, Here Comes the Bride, The Old Gray Mare, etc. Some inspirations for song are outlined in song: love, sailing, trains, the West, motherhood, etc., but "we never sing about brains." Finally, an example of how a simple melody can be expanded into a symphony: an elaborate version of the simple tune that opened the lesson