Tetrodotoxin is a potent neurotoxin primarily found in certain species of pufferfish, as well as in some other marine animals like blue-ringed octopuses and newts. It blocks sodium channels in nerve cells, preventing the transmission of nerve impulses, which can lead to paralysis and, in severe cases, death. Exposure to tetrodotoxin can occur through ingestion of contaminated seafood or through bites from toxic animals. Symptoms of poisoning include numbness, dizziness, and respiratory failure. There is no known antidote, making prevention and careful handling of potentially toxic species crucial for safety.