What is the very poisonous fish that Japanese like to eat? And why do they bother?
That would be fugu, which describes certain species of puffer fish. Some of the fish's organs contain tetrodotoxin, an extemely powerful poison—one fish contains enough to kill 30 people. Victims become paralyzed to the extent that they are unable to breathe and die of asphyxiation. There is no known antidote.
In Japan, fugu chefs require special training and licenses, to be sure that they are able to remove the poisonous organs before preparing the safe parts for consumption. In theory, fugu prepared by a trained professional should be entirely safe to eat; most cases of fugu poisoning are caused by home preparation by unlicensed chefs.
Why do they bother? Many people like the taste, which is described as being subtle, delicate, and unique. Some like the pleasant buzzing sensation that comes from trace amounts of the poison at safe levels. And no doubt some are tempted by the fish's mystique, the allure of cheating death.
—The Fact Monster