“I think it is a book of hope,” Eric Carle said about his book The Very Hungry Caterpillar. “You, an insignificant, ugly little caterpillar can grow up and eventually unfold your talent, and fly into the world.”

The children’s book author and illustrator Eric Carle died last week at the age of 91. Almost everyone knows his masterpiece and most famous book, The Very Hungry Caterpillar. It’s been translated into 70 languages and has sold something like 55 million copies worldwide. That’s a lot of apples, pears, plums, strawberries, pickles, pieces of salami, lollipops, and cupcakes for one small caterpillar to eat its way through, no matter how hungry.

But did you know the caterpillar was originally a worm, and that the book’s title started off as A Week with Willie Worm? It’s a good thing that Carle’s editor thought a ravenous worm might not be the best hero for a kids’ book—what are worms most famous for eating?—and suggested he switch to a caterpillar, because that gave him the idea for his twist ending. “Butterfly!” he shouted.