The Mad Hatter poses a famous unanswered riddle in Alice’s Adventures in Wonderland: “Why is a raven like a writing desk?”

W.S. Gilbert poses another one in the Gilbert and Sullivan operetta The Yeomen of the Guard. The jester Jack Point asks, “Why is a cook’s brainpan like an overwound clock?” The Lieutenant impatiently says, “A truce to this fooling,” and Jack withdraws, saying, “Just my luck: my best conundrum wasted.”

“Like many in the audience, I have often wondered what the answer to that conundrum is, and one day I put a question about it to Gilbert,” wrote Henry A. Litton in The Secrets of a Savoyard (1922). “With a smile he said he couldn’t tell me then, but he would leave me the answer in his will.”

“I’m sorry to say that it was not found there — maybe because there was really no answer to the riddle, or perhaps because he had forgotten to bequeath to the world this interesting legacy.”