If you grew up in the United States or likely anywhere else in the English-speaking world, you’ve heard the tale of Humpty Dumpty, the egg-man pictured above from a 1904 illustration. If you haven’t, for some reason or another, here’s a common version of the nursery rhyme:

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.

It’s a short, simple, AABB rhyme. Easy to remember, too, so it’s no mystery as to why it’s well-known. But there is a mystery buried within those twenty-six words, or, more accurately, omitted from them. Everyone agrees that Humpty Dumpty is an egg. But the rhyme doesn’t actually tell us that.

Where does that come from?

On its face, there’s no reason for the rhyme to be about an egg or egg-man. If any one of us had a great fall off a wall at the time of king’s men riding on horseback, there’s good reason to think that we’d be irreparably broken. And to the extent that the Humpty Dumpty story is a parable, “don’t sit atop walls” is a much better lesson than “try not to turn into an egg-person.” So that’s probably not what’s going on here. The origins of the rhyme date back to at least 1797, but the original words, below, similarly do not say that the wall-sitting Mr. Dumpty is an egg:

Humpty Dumpty sat on a wall,

Humpty Dumpty had a great fall.

Four-score Men and Four-score more,

Could not make Humpty Dumpty where he was before.

But by 1871, Humpty Dumpty’s oval-shaped status appears well entrenched. That year, Lewis Carroll published “Through the Looking Glass,” the sequel to “Alice’s Adventures in Wonderland” and a classic in its own right. At one point, Alice sees an egg-like thing in the distance, and walks toward it:

HOWEVER, the egg only got larger and larger, and more and more human: when she had come within a few yards of it, she saw that it had eyes and a nose and mouth; and, when she had come close to it, she saw clearly that it was HUMPTY DUMPTY himself. ‘It can’t be anybody else!’ she said to herself. ‘I’m as certain of it, as if his name were written all over his face!’

Because really, even in Wonderland or in that world beyond the other side of the mirror, there aren’t a lot of egg-men.

The likely explanation, per the trivia-mavens at the Straight Dope, is that the rhyme was never intended to be a parable. Rather, they find, it was a riddle — “riddling rhymes were a popular source of entertainment for many centuries.” Going to the rhyme itself, the earliest known version references “four-score Men and Four-score more” — that’s 160 total — is the rhymes way of saying that despite dramatic amounts of available resources, the problem surprisingly couldn’t be solved. The way it makes sense is if you “solve” the puzzle, concluding that Humpty Dumpty wasn’t any regular man, but one with the cranial fortitude of an egg. (In fact, in “Through the Looking Glass,” Humpty Dumpty himself finds it ridiculous that anything could happen to him, because if he fell, the king would surely take steps necessary to repair him.) Makes sense, kind of.

And while there’s some evidence that may not be the case — here’s a picture from an 1877 children’s book showing Humpty as a young, non-egg boy — the image above buttresses the claim set forth by the Straight Dope. The image, from a 1902 Mother Goose book, clearly identifies Humpty Dumpty as an egg and does so in a way to suggest that the rhyme is a riddle. It’s just one you already knew the answer to — but, probably not why.

Bonus fact : Mother Goose never existed — she’s a fictional poet (perhaps named as such due to the popularity of Old Mother Hubbard) who acts as a stand-in for the nanny-ish, motherly figure. References to “Mother Goose” (in various languages, most often French) date back to the early-1600s, but don’t tell that to tour guides in Boston. Many highlight the gravestone of a “Mary Goose,” who died in 1690 in her forties (see the gravestone here), as being the final resting place of the Mother Goose, but that’s not rooted in anything close to verifiable history.

From the Archives: And The Oscar Doesn’t Go To: When a movie’s director wanted to be credited as “Humpty Dumpty.”

Related: A collection of Mother Goose nursery rhymes. 4.8 stars on 85 reviews.