When asked to name a poison, people may well think of cyanide, arsenic or strychnine. But these are not the most toxic substances known. More poisonous than these, but still not near the top of the tree, is tetrodotoxin, the pufferfish toxin that poisons around 50 Japanese people every year. The fish is a delicacy in Japan, but can be lethal if prepared incorrectly. Incidentally, this was the poison favoured by evil assassin Rosa Klebb in James Bond film From Russia With Love. It also crops up in the blue-ringed octopus and was more recently discovered in tiny frogs in Brazil.