“My favorite gems in his notebooks are his to-do lists, which sparkle with his curiosity. One of them, dating from the 1490s in Milan, is that day’s list of things he wants to learn. ‘The measurement of Milan and its suburbs,’ is the first entry. This has a practical purpose, as revealed by an item later in the list: ‘Draw Milan.’ Others show him relentlessly seeking out people whose brains he could pick: ‘Get the master of arithmetic to show you how to square a triangle… Ask Giannino the Bombardier about how the tower of Ferrara is walled… Ask Benedetto Protinari by what means they walk on ice in Flanders… Get a master of hydraulics to tell you how to repair a lock, canal and mill in the Lombard manner… Get the measurement of the sun promised me by Maestro Giovanni Francese, the Frenchman.’ He is insatiable.

Over and over again, year after year, Leonardo lists things he must do and learn. Some involve the type of close observation most of us rarely pause to do. ‘Observe the goose’s foot: if it were always open or always closed the creature would not be able to make any kind of movement.’ Others involve why-is-the-sky-blue questions about phenomena so commonplace that we rarely pause to wonder about them. ‘Why is the fish in the water swifter than the bird in the air when it ought to be the contrary since the water is heavier and thicker than the air?’

Best of all are the questions that seem completely random. ‘Describe the tongue of the woodpecker,’ he instructs himself. Who on earth would decide one day, for no apparent reason, that he wanted to know what the tongue of a woodpecker looks like? How would you even find out? It’s not information Leonardo needed to paint a picture or even to understand the flight of birds. But there it is, and, as we shall see, there are fascinating things to learn about the tongue of the woodpecker. The reason he wanted to know was because he was Leonardo: curious, passionate, and always filled with wonder.”

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Pulled from the intro to Walter Isaacson’s new biography, Leonardo da Vinci.

Some thirty chapters and five-hundred pages later, Isaacson has us at the book’s coda, “Describe the Tongue of the Woodpecker.” Here’s that coda, in full:

The tongue of a woodpecker can extend more than three times the length of its bill. When not in use, it retracts into the skull and its cartilage-like structure continues past the jaw to wrap around the bird’s head and then curve down to its nostril. In addition to digging out grubs from a tree, the long tongue protects the woodpecker’s brain. When the bird smashes its beak repeatedly into tree bark, the force exerted on its head is ten times what would kill a human. But its bizarre tongue and supporting structure act as a cushion, shielding the brain from shock.

There is no reason you actually need to know any of this. It is information that has no real utility for your life, just as it had none for Leonardo. But I thought maybe, after reading this book, that you, like Leonardo, who one day put ‘Describe the tongue of the woodpecker’ on one of his eclectic and oddly inspiring to-do lists, would want to know. Just out of curiosity. Pure curiosity.