Galileo's "Dialogue on the Two Chief Systems of the World," includes a discussion about dropping balls from the mast of both a moving ship and a ship at rest in order to test the theory of inertia. If sailors actually had performed the experiment, believing with Aristotle that a cannonball dropped from the mast would fall harmlessly into the wake of the ship, why were no reports made to the contrary? This OER includes a cartoon with an answer to the question.