A floating bowling ball? No way! There is no better way to get students' attention and reinforce the need for conceptual understanding than with a discrepant event like this. Density is a central concept in chemistry and physical science from middle school to college. But often, particularly at the high school and college levels, we think students understand density simply because they can solve density problems. In this article, the authors describe an activity in which students explore the relationship among the mass, volume, and density of various sports balls.