The story in three lines. Beto finds that only an egg fits an egg cup. Margit draws a protein with an empty pocket, because the letters say nothing about what goes inside. Kemi's photograph shows a small partner sitting exactly in the pocket, which Beto nearly wipes off as dirt.

One thing to do at the table. Collect small things: a coin, a button, a bead, a pea. Draw outlines of a few hollows on paper: an egg cup, a bottle top, a keyhole shape. Measure and decide which thing fits which hollow before you try.

The grown-up layer. Many proteins work by holding a small partner in a pocket shaped for it, such as a metal atom or a sugar. A prediction made from the protein's own chain shows the pocket but not the partner, because the partner is not written in the chain. Experiments can show both. This is a good example of why predictions and experiments are used together.

For the ride home. Ask: why couldn't Margit draw the smudge?