The story in three lines. Danya wonders why a pen spring curls. Margit, the Sketcher, draws a protein from its letters alone: a spiral in ink, a zigzag in pencil. Kemi, the Photographer, shows the real thing: the spiral is right, and the zigzag lies beside a partner Margit never drew.

One thing to do at the table. Before you look at something, draw it from memory: a bike, a kettle, the back of a coin. Use a pen for the parts you are sure of and a pencil for the rest. Then look, and talk about which pencil parts were right.

The grown-up layer. Proteins are long chains of building blocks that fold into shapes, and the shape decides what the protein does. Computers can now predict many shapes from the chain alone, and say how confident they are about each part. Experiments, such as freezing proteins and imaging them, show what is really there. The two together are the modern way of knowing a protein's shape. The pencil-and-ink idea matches how the Fold Commons Viewer marks predicted and measured parts.

For the ride home. Ask: was Margit's pencil zigzag wrong?