"Four little houses closed up tight. Let’s open the windows and let in some light"
See what you like! The idea of using little houses is very easy to understand. Everyone at one point in their life have pass through multiple houses. Unfortunately I was not able to find small houses, so I decided to go with small fishes. The gills of the fishes allow them to breath the oxygen dissolved in the water. Water passes through their mouth and eventually it would pass through the gills.