Poisonous Mushrooms.

It goes almost without saying that some Mushrooms are poisonous, not edible and can give you an extremelly bad reaction to them. You are pretty safe while shopping in a supermarket, a little less so while getting Mushrooms in a Market, and further less so when you are foraging. The key is knowledge. Buying a guide to recognise your Mushrooms is essential but I will say also there, that another opinion, a second one, can be ever so helpful in the case of a doubt.