This article accompanies the fable
Lennon's choice of an onion is hilarious, for glass has a long history as a metaphor.
The glass metaphor was well known in Europe from the 15th-17th centuries, when sufferers imagined their body was made of glass and that it could shatter at any moment.
Cervantes makes use of this in his short story El licenciado Vidriera (The Lawyer of Glass, aka The Glass Graduate). A young man is given a love potion and it drives him mad – he is convinced that his whole body is made of glass. But his "madness" allows him to make wise pronouncements (meaning clearly he is not mad) and he develops a large following. He loses his following when - ironically - he is cured and he recovers his sanity.
Is glass a triumph of Man's ingenuity over the raw materials of Mother Nature? Was God to be found within? Peering into crystal balls, the seers of medieval times hoped to find the grail; alchemists stared in at the phoenix and hoped stone would transform into gold; in Murano they caught fire in a glass; at Chartres the holy spirit streamed in through the stained glass windows. Even in the scientific age when it became the looking glass and the hourglass, it retained its magic.
It all shattered during Kristallnacht, for glass could be whatever you wanted it to be, and lately it has been appearing as Pyrex dildos in the bedroom and on the coffee table. A metaphor for the ages.