Randomly occurred to me that I eat an excessive amount of food and I'm rarely full, and that got me thinking that if by some freak accident I were stranded on an island or in an isolated area with family or friends I'd probably be forced to turn to cannibalism. To avoid that I've found this page on doing taste tests, to see which plants are edible or not. http://www.ehow.com/how_2156033_perform-universal-edibility-test.html

Basically you don't eat anything for half a day, you cut up the plant into it's main parts, you test each part for fifteen minutes at a time by pressing them against your lips, and then if there's no stinging or burning you can move on to testing them the same way but against your tongue.

After that if there's no stinging or burning reaction you can take one portion of the plant and chew a small amount without swallowing. You wait three minutes, and if there's no reaction you can swallow it. Once you do that you've got to wait another half day until you're sure there's no reaction. If there is one you've got to throw it up somehow.

If it's successful, you eat a larger amount of that plant, and wait ANOTHER half day, waiting to see if your stomach commits suicide. Obviously then if that produces no reaction that part of the plant is safe! But then that still leaves the other parts to test... like the leaves, stem, flower, fruit... it's a good thing we can survive eight weeks without food!