Nina investigates how divers breathe underwater with the help of Felix, her touch neuron. Engineers Josh, Dan and Jack visit Nina in her workshop and discover that there isn't enough air for people to breathe underwater. They go to a swimming pool where they try snorkelling and find out that you can use a tube to breathe underwater. Next they visit an aquarium and see divers using tanks full of air. The tanks let them go deep underwater and stay there for a long time. Show less