In this article, the author describes a simulation of a coevolutionary "arms race" and introduce a way of teaching it that lets students use the theory of natural selection to explain the outcomes of the simulation. The simulation uses the numerical cards from an UNO[R] playing card deck to represent the speeds of individuals in populations of predators and their prey. Simple descriptive statistics are then used to illustrate changes in the two populations. He discusses the simulation process and the rules of play. He also presents a post-game discussion. (Contains 2 tables.)