Like many legumes, the seemingly innocent lima bean should not be eaten raw – doing so can be lethal. (And who wants to die in such an ignoble way as death by lima bean?) Also known as butter beans, the legumes can contain a high level of cyanide, which is part of the plant's defense mechanism.
Here in the U.S. there are restrictions about cyanide levels in commercially grown lima bean varieties, but not so in less developed countries, and many people can get sick from eating them. Even so, lima beans should be cooked thoroughly, and uncovered to allow the poison to escape as gas. Also, drain the cooking water to be on the safe side.