I was bored and started thinking what is the deadliest substance/thing that could kill a human adult that is also either very tiny. I came up with ricin, as I understand only a few grams of the stuff could be deadly, although I might be wrong. I think that was the toxin used in the spy killings when a spy stabbed someone with an umbrella tip that injected a tiny ball full of ricin.
Okay, so you get my drift. What is the smallest amount of something that can kill an adult?