A recent posting on water caltrops made me think of this. What non-meat food stuffs are there that have to be cooked before they can be eaten. Not just stuff that is traditionally cooked, but things that can make you sick if not cooked properly.
I don't know of many common ingredients in Western cooking, but I've encountered this a couple of times with Asian ingredients (it's a good thing I google stuff before cooking), and it would be useful to have an international list.
The ones I know are
Fresh bamboo shoots; needs to be well cooked or is very bitter. I'm not sure if it will actually make you sick.
Water caltrops; need to be cooked to kill a common parasite.
Taro; both leaves and roots must be cooked to break down a toxic chemical.
Mountain Papaya (different than the usual tropical papaya); must be cooked to break down a chemical that irritates the mouth and throad.
Any others? And the reason why it has to be cooked.