If you simply MUST eat strange plants, test them first by crushing a berry/leaf and rubbing the juice on your skin. If you get any discoloration, blistering, etc, then you will NOT enjoy eating it.

Very rarely are things lethal like that. Poison edibles tend to taste awful, and if you start with a small amount you will learn whether it makes you sick.

Now mushrooms on the other hand? No idea how they figured it out.