Poisonous species are organisms that produce toxic substances that can harm or kill other organisms when ingested, touched, or otherwise interacted with. These toxins can serve as a defense mechanism against predators or as a means to capture prey. Examples include certain types of frogs, snakes, and plants. Not all poisonous species are dangerous to humans, but some can cause serious health issues or even death. For instance, the pufferfish contains a potent toxin called tetrodotoxin, while the deadly nightshade plant has alkaloids that can be harmful if consumed. Understanding these species is crucial for safety and ecological balance.