Death cap are tasteless. There is alot of seriously poisonious stuff out there that is completely tasteless, odourless, or sweet and juicy. And there is also alot of edible plants that taste or smell pretty disgusting.
Blackthorn flowers are prefectly edible. The website that was quoted by Steve R also as well as saying they have TRACE amounts cyangenic glycosides goes on tell you how to make tea out them later.
I far as I know no native member of the prunus group causes poisoning. The problem species are cherry laurel, chokecherry and american wild cherry. Most of the serious problems occur in ruminants not humans. We have a stong acid stomach and the liver of an omnivore and we are actualy really good at breaking down poisons. We are not sheep or cows, the acid in our stomachs pretty much stops the hydrogen-cyanide from coming out of the plant. Humans are evovled to eat plants that contian small amounts of amygdalin.
All I do is trust my liver, eat wild foods, smoke, drink beer, look up whether a plant has ever poisoned anyone ever, and remember that nutmeg is 2% benzene.