The story in three lines. The spark takes Lan and Inkling to a village of houses on posts at the edge of a marsh, about five thousand years ago, where a boy must bring a heavy oak post from the forest before the rain floods the path. Dragging on a flat board fails; log rollers work but keep falling out the back. Lan asks whether the round thing could come with them, and the boy fixes two round slices to a stick so they stay under the board.

One question to ask. "Why did the flat board drag?" Listen for "all of it was rubbing" or "it dug in." Then ask: "What was wrong with the rollers, even though they rolled?"

One thing to do at the table. Push a book across the table. Then put three round pencils under it and push again. Watch what happens to the pencils at the back. Then try a toy car. What does the car have that the pencils don't?

The grown-up layer. A flat surface rubs along its whole length; a round one touches along a thin line and turns instead of scraping. Rollers are an old idea; keeping the round thing attached on an axle is the step that makes a wheel. The real wheel found in the Ljubljana Marsh in 2002 (about 5,100–5,350 years old) had a square-ended oak axle, so wheel and axle turned together, as the boy makes them in the story. Nobody knows who made the first wheel. The story is a guess about how it might have felt to work it out.

Let your child tell the story back first. Telling it back is how the letter goes on the anvil.