We reviewed what we have been learning about liquids by looking at a cup of water and then adding food coloring. We looked at how it moved, thinking back to how it moved in the tests we made in "Swirling Colors." This revealed that it was indeed plain water. We poured this into an empty plastic bottle. The coloring mixed all through the water. We looked at another clear liquid, but when we poured this into the bottle, it did not mix with the water. Thinking back to "Raindrops and Oil drops," they could guess that the new liquid was oil (mineral oil, in fact.) We screwed on the top tightly and watched the "ocean in a bottle," discovering that no matter how much they tried to mix them, they never could mix the two liquids.