i wonder if that guy knew some leaves could be harmfull. the info. you just gave is new to me. i guess you cant judge a leaf by the tree it grows on.
Of course, we don't usually eat the leaves of these plants. Tobacco itself contains many potentially lethal alkaloids.
Livestock, however, can quickly get into trouble, if their preferred graze is in short supply, and they consume the leaves from the wrong fallen tree.
Most of these also have a dose threshold, beneath which they can be consumed without effect. There is a well documented case of a man who loved the taste of apple seeds, which he ate on a regular basis. Then he decided to collect them until he had a nice supply. He ate a cupful of his saved apple seeds, and immediately died.
Goats, and other browsers (as opposed to grazers) can usually eat all sorts of poisonous plants, because they only eat a little of each available plant. If they are confined in a area with only a toxic plant (say, choke cherry), they will eat enough of it to cause death.
Humans consume all sorts of toxic plants: most of the cabbage family, mustards, grapefruit, tomatoes, potatoes, turnips, parsley root, coffee, cocoa, tea leaf, kidney beans, etc. If a diet focuses on some of these, they can cause all sorts of illnesses, from kidney or liver failure, to thyroid suppression. Because of threshold toxicity, eating a variety of different foods minimizes the risk.
Bob