TIL

In 2009 scientists at the University of Eastern Piedmont in Italy claimed to have identified hemlock water dropwort (Oenanthe crocata) as the plant responsible for producing the sardonic grin.
This plant is the candidate for the "sardonic herb," which was a neurotoxic plant used for the ritual killing of elderly people in pre-Roman Sardinia.
When these people were unable to support themselves, they were intoxicated with this herb and then dropped from a high rock or beaten to death.