Nina investigates why rivers are wiggly - with the help of Belle, her hearing neuron and Felix, her touch neuron. Explorers Amelia, Patrick and Radiyya visit Nina in her workshop and discover that rivers move rocks and sand. Next, they have a go on a river rapids ride and find out that water moves fast and slow at different places. Lastly, they find out that the fast and slow water is what makes a river change shape and makes it wiggle.