The abundance of online resources that students have access to makes it difficult to determine whether the information they find is accurate. Several online sources have claimed that hamburgers from fast-food chains do not decompose, and we developed two exercises that allow students to (1) test this claim, (2) learn about fungi, and (3) reflect on their eating habits. In both exercises, we inoculated fast-food items with the fungus Rhizopus stolonifer . The first exercise was a controlled experiment with hamburgers, and the second was a screening trial in which all students brought in their own fast-food items. In both exercises, animal-based products and fatty baked products (e.g., biscuits) allowed R. stolonifer to grow, while condiments and bread products tended to inhibit growth. Our students indicated that they would be more critical of online information and that they would eat less fast food. These exercises met our objectives and engaged our students, and we encourage others to develop exercises that examine online claims.