Inflatable Fish

Because pufferfish are slow and vulnerable to predators, they use the elasticity in their stomachs to swallow water and air to inflate themselves into an inedible ball several times larger than their normal size. These fish also contain a natural toxin called tetrodotoxin that can be lethal to fish and other animals. In fact, one pufferfish holds enough toxins to kill 30 adult humans. Some predators, like tiger sharks and sea snakes, aren't harmed by the pufferfish's natural toxins though.