The nursery rhyme Humpty Dumpty was originally a riddle

Humpty Dumpty sat on a wall,

Humpty Dumpty had a great fall.

All the king's horses and all the king's men

Couldn't put Humpty together again.

Incredible Egg Shell Carving by Wen Fuliang

The answer is an egg and, for a long time, Humpty Dumpty stood for something that, once broken up, can never be made whole again. Unless that thing was meant to be broken up in order to be put together again – a jigsaw puzzle.

Internal Membrane Of Hen Eggshell

http://blog.ultimateglobes.com/2013/08/global-puzzle.html