Natural Bushcraft - The True Spirit of Bushcraft

I went out walking down a river a few days ago with an experienced bushman. He showed me sea beet, brought it home and put in a curry and it was delicious. I had a good look at the sea beet and tried to commit it to memory. A few days later I went walking alone along a different river and spotted what I was sure was sea beet. I picked it, brought it home, and compared it to pictures on line. I'm not silly enough to go eating random things I find out walking, but I am determined to learn more about natural world around me, so I double checked the description and the pictures, and decided to boil it up and add it to my evening meal. After only a few bites my mouth began to burn, especially under my tongue. After a few more bites I had the overwhelming feeling of "Uh oh, I shouldn't be eating this!" My mouth was burning, my tongue was swollen, my thought was red and swollen, I broke out in a sweat and my face was burning red. I induced vomiting, which wasn't difficult because my stomach also felt pretty unsettled. After a few minutes most of the symptoms subsided and I just felt a little sore around the mouth, and very, very stupid. I took some photos of the left over leaves and sent them to my bushcraft friend, and he informed me they were Arum Maculatum. Now, reading about how poisonous they are I think myself very lucky indeed. My first foray into foraging besides apples and blackberries and I go eating poison leaves, but I live to tell the tale and I certainly have a greater respect for whats growing around me. Knowing what to eat and not what to eat is a skill I will surely devote more time and energy into from now on.

i saw that the birds had eaten some of the berries so i tried one. it tasted surprisingly good. in what way are the berries and leaves poisonous/ what poison what is the effect?