Scientist Nina and her young experimenters discover the amazing ways that things can change and react in the everyday world.

Nina investigates why onions sometimes make us cry, with the help of Luke, her sight neuron. Experimenters Matthew and Tia visit Nina in her science lab and use their senses to work out that onions only make us cry when they are cut open. Under Nina's microscope, they see that an onion is made up of lots of tiny cells. Nina explains that these are full of onion juice. She cuts into a model of an onion cell making the juice spray up in the air.

Then they go to visit a tropical greenhouse and see tiny droplets of water being sprayed into the air. These droplets are really hard to see because they are so small and so are the droplets of onion juice that get into our eyes. Back in the lab, the Experimenters find out that onion juice stings our eyes because it is a weak acid. But our clever eyes make tears to stop the juice from being stingy and wash it away. Show less