I think this is a better question for /r/Anthropology

Poisonous almost never means instantly lethal. In any kind of reasonable dose, most plants that are considered poisonous will leave you alive but sick enough to encourage yourself and others to learn from your mistake.

"It's important to understand that accidental plant poisoning is very unusual and only very rarely do people suffer serious harm. Death from accidental ingestion of a poisonous plant, in its natural state, is exceptionally unusual." Source : www.thepoisongarden.co.uk

*determine, sorry english isn't my native language