The Puffer fish is considered the second deadliest vertebrate in the world, after the Golden Poison Frog. The common image we have of this creature is that it inflates when threatened. I had a pet Fugu a few years ago but it didn't inflate at all. It died four hours after the transaction.
What makes Fugu so popular is the lethal toxin in its liver, skin and the ovaries, and the fact that the Japanese treat it as a delicacy. Pretty ironic I guess? By the way it is extremely expensive and prepared only by trained, licensed chefs who, like all humans, occasionally make mistakes =P.
Of course, don't go around scaring puffer fish because a puffer fish could only perform a limited number of inflation in its life.
The stomach expands to nearly a hundred times its original volume, and the fish's spine, already slightly curved, bends into an upside-down U shape, and all other internal organs become squeezed between the fish's backbone and its rapidly expanding stomach. Meanwhile, the fish's skin is pushed out, obscuring most of the puffer's features-http://divingintaganga.blogspot.com/2010/09/how-and-why-pufferfish-inflate.html
|Image: Sally J. Bensusen. American Museum of Natural History.|