The Porcupine Puffer-fish.

The Puffer fish are the second-most poisonous vertebrates in the world, after the golden poison frog. they contain toxin (called tetrodotoxin)in their internal organs that can be 1200 times stronger than cyanide, and one puffer fish has enough toxin to kill 30 men.

An interesting defense mechanism the porcupine fish has is the ability to inflate and swell up their bodies by swallowing water or air, becoming rounder. They do this to prevent predators from eating them if they don't have a wide enough jaw span. If that doesn't work, the puffer-fish has sharp spines, which expand outward when puffed up.

However, puffing up for this porcupine puffer fish is equivalent to a heart attack in a human and is extreme stress and 95% of the time leads to death at an early age, so it can only puff up 3-5 times in its whole life.

FUN FACT:

Did you know that scientists have discovered dolphins actually get 'high' off the puffer-fish toxins?

It has been observed that adolescent dolphins will tend to find a puffer fish and chew on it 'gently', then pass it onto its peers to chew on as well.
Apparently in doing so the dolphins will intake a small amount of the toxins, producing a narcotic effect,which then leads the young dolphins to start acting 'high', like swimming around stupidly in a daze, mesmerized by their own reflections in the water, much resembling the effects that alcohol has on an average human.

Which is to say, dolphins get drunk on puffer-fish toxins.

{click here to read a full article and here to watch a video on this phenomenon}