As the German writer Goethe observed, ‘there is no such thing as poison, it all depends on the dose’. Poisons have featured in many murder cases, and for the determined poisoner, history has shown that there is always a vast range of materials at hand. Arsenic used to be one of the most widely available poisons. For the prospective poisoner, few substances could match it. It looks so harmless, like flour or sugar, and its virtual lack of taste means it is easy to disguise in drink or food.