A 34-year-old man presents to the emergency department with blurred vision, dry mouth, and progressive, symmetric descending weakness. He reports that his symptoms began with diplopia and difficulty swallowing, and over the last 12 hours, he has experienced increasing weakness in his arms and legs. His past medical history is unremarkable, but he mentions that he recently ingested home-canned vegetables. His vital signs are stable with a blood pressure of 128/76 mm Hg, heart rate of 82/min, respiratory rate of 18/min, and temperature of 37°C. Which exotoxin is most likely responsible for his clinical presentation? Key clinical features: - Blurred vision and diplopia - Dry mouth - Progressive, symmetric descending paralysis - History of ingestion of improperly canned food