Comment by schoen

There are a lot of examples of this in the book The Secret of Our Success (which argues that human cultures have a lot of culturally-evolved knowledge which individuals would be very unlikely to develop in a single generation, and which often provides benefits for reasons that aren't consciously understood by the actual members of the culture, while occasionally including some noise or bad advice).

Many of those are traditions or ritual behaviors that decrease the chance of poisoning, sometimes subtle chronic poisoning rather than obvious acute poisoning.