This paper describes a working-model demonstration of Ernest Rutherford's 1911 experiment about the nature of atoms. In this demonstration, a model of an atom is constructed inside a sealed cardboard box. Ping-pong balls are fired into (and sometimes through) the box to determine the structure of the atom. Like Rutherford's experiment, this demonstration shows that atoms are mostly empty space. Use this demonstration as an opportunity to discuss the nature of science.