Puffer fish

Puffer fish or Blow fish live in warm waters around the world. What makes a Puffer fish so intresting is that is can "blow up" about 8 times its orginal size. This happens when it feels threatened by a predator. They have very flexible stomaches and can swallow lots of water or even air very quickly. Even if a predator ate a Puffer fish the poison inside it would kill the predator. The poison inside the Puffer fish is 1,200 times stronger than cyanide. There is also no known antidote. However, there is a dish in Japan called fugu which uses Puffer fish meat. Many times people have died eating it because it wasn't prepared correctly.

photo credit: 

   http://www.tvacres.com/chemicals_tetrodotoxin.htm

Source: 

http://animals.nationalgeographic.com/animals/fish/pufferfish/