Students are provided with a mystery concerning dogs that are paralyzed. This motivates a laboratory exercise to measure parameters from the dog's “blood” to determine whether the paralysis is due to pesticide poisoning or an autoimmune attack on nerve myelin. Most of the materials are available from the grocery store. The real-world nature of the problem, and the mystery, engages the students in thinking about nerve, muscle, and immune system function. Alternative versions require less familiarity with physiology and can be used as engagement activities to encourage learning laboratory skills and experimental design or as motivation for learning nerve and muscle physiology.