So we figured out that as humans, we eat dead animals and plants (unless we're a vegetarian or vegan), and that got us wondering what the raccoon that Mrs. Brinza found on the side of the road eats. Through a reading, we discovered that a raccoon eats dead animals and plants, and by developing a model, we know that whatever does the eating gets bigger and grows/develops new parts, and that whatever got eaten gets smaller/disappears into the organism that ate it!
And then we built models for humans...