A simple and short contact with the skin can already cause paralysis.
Monkshood is famous for its outward appearance and people even plant it in their garden (we dissuade from this!). However one must not forget the toxicity and therefore danger of this plant! All parts of the plant offer the poisonous substance Aconitine what is one of the most poisonous substance a plant can have. A dose of 100-200 g can already cause death! And a simple contact with the skin (what happens quite easily) can effects paralysis!
This fact can have great problems especially for horses. Generally it is hard to find the origin of paralysis what makes the medicinal treatment difficult. In this special case the only cure is the exact antidote what makes the cure even more difficult and the plant more dangerous.
In Europe the monkshood has yellow or blue flowers.
In general one needs to control all places where horses are without supervision (e.g. pastures) if there are any poisonous plants.