Viruses are all around--and within. They replicate inside the cells of living organisms. An estimated 1.6 million to 40 million of them occupy each cubic meter of the air people breathe. The activity described in this article helps students understand how the structure of a virus allows it to infect a specific set of organisms and cell types. Students also explore the relationships between viral components and mechanisms of replication. This activity uses the techniques of active learning to engage students with a tactile representation of a biological process, making them active participants in the classroom. A student engaged in active learning discovers, processes, and applies new information to solve problems. While the teacher acts as facilitator or coach, students assemble their own understanding of the concepts. Students actively engaged in the classroom may attain higher levels of achievement within all socioeconomic backgrounds.