No smiling matter

A couple of miles up the road and you come to this outlying settlement of the nearest village, a cluster of houses around a grassy green watered by a couple of fast-flowing streams running along stone-built channels. There's an old village pump and lower down a disused baptism tank belonging to a nearby chapel. Nowadays the houses have piped water and the streams are just reminders of how things used to be, in fact they are choked with vegetation: thick stems with their roots in the water and dark green foliage bearing white inflorescences not unlike cow parsley but larger and sturdier.
It's not cow parsley, it's hemlock water dropwort, Oenanthe crocata, common enough in watercourses and damp places, and deadly poisonous to animals and humans unwise enough to sample it - especially the thick white roots which resemble parsnips. It's hard to think why anyone would be tempted to eat them but a few years ago a group of students camping in Scotland adventurously concocted a curry with what they imagined to be 'water parsnips'. Four of them had to be rushed to hospital and although they all survived the symptoms included grand mal fits, hallucinations, nausea and fever. Details here.

The plant contains oenanthotoxin which is similar to strychnine and produces convulsions, renal failure and ultimately death in many cases. Its signature effect is a tooth-baring rictus grin produced by the facial paralysis the poison causes. It is only relatively recently that this has been understood to solve an age-old mystery, the 'sardonic smile' that was reported by Homer to have been worn by the unfortunate victims of the ancient Sardinians' strategy for dealing with murderers and old people who could no longer support themselves. Dosed with a paralysing herb, these unwanted members of society would be dropped off a cliff or beaten to death, apparently embracing the afterlife with a grin of pleasure...
(Ironically, oenanthotoxin is now thought to have potential as a face-smoothing anti-ageing potion like botox so maybe taken therapeutically it could help defer whatever fate old age has in store for us as the options for geriatric care in our own society become increasingly grim.)

Read more about this here.