Amphibian
Newts in the genus Taricha has a poison called tetrodotoxin, a neurotoxin. Scientists believe that toxins in newts are caused by bacteria in the genera Pseudoalteromonas, Pseudomonas and Vibrio. Because of this, the newts do not have a lot of predators. However, some species of snakes have develop a resistance. This means that they can eat newts without the toxin hurting them. It is a case of co-evolution.