Poisonous substances are materials that can cause harm or illness when they enter the body. These substances can be found in various forms, including chemicals, plants, and animals. Common examples include carbon monoxide, arsenic, and certain mushrooms. The effects of poisoning can range from mild symptoms, like nausea, to severe reactions, such as organ failure or death. Many poisonous substances work by disrupting normal biological processes. For instance, some toxins can interfere with the nervous system, while others may damage cells or organs. It is important to recognize and avoid exposure to these harmful materials to ensure safety and health.