A poison, or toxin, is a substance that can cause harm or illness when it enters the body. Poisons can be found in various forms, including chemicals, plants, and animal venoms. They disrupt normal biological functions, leading to symptoms that can range from mild to severe, depending on the type and amount of poison. Many organisms produce toxins as a defense mechanism or to capture prey. For example, some species of frogs and snakes have potent venoms that can incapacitate their predators or prey. Understanding how poisons work is crucial for fields like medicine and toxicology, which study their effects and develop treatments for poisoning.