The story in three lines. Danya watches oil drops gather in salad dressing. Margit predicts that a protein's twelve oily links pack inside, and Kemi's photograph shows eleven inside and one at the edge. The odd one out is touching a partner protein, so it is still out of the water.

One thing to do at the table. Shake oil and water in a clear jar with a lid. Watch the drops gather. Ask: are the drops looking for each other, or is the water pushing them together? Add a drop of washing-up liquid and watch what changes.

The grown-up layer. Water molecules hold on to each other strongly, so oily things end up gathered together. In a protein, this pushes oily building blocks into the middle and is one of the main reasons proteins fold. Oily patches on the surface are often where a protein meets a partner. The story is careful with words: the oil does not want anything; the water arranges it.

For the ride home. Ask: was the one outside link a mistake in Margit's drawing?