Subject: Food Chains – Arnold and Keesha are in trouble when they forget an assignment to bring in two things that go together. He has a soggy shoe with pond scum he stepped in on his way to school. Keesha has only the tuna fish sandwich she brought for lunch. Ms. Frizzle is delighted at this brilliant combination! A field trip to the ocean becomes a search for the connection between these two unlikely objects. The bus shrinks and travels through the ocean food chain – getting eaten along the way!