Have you heard the one about Bulgarian journalist, Georgi Markov? Like a plot-line straight out of a Bond film, says Hank Green in the episode of SciShow above, Markov was just walking across a bridge in London one day, minding his own business, when all of a sudden, he felt a slight sting in his right thigh. The well-known Communist defector, who was at the time working for the BBC, turned around, and saw a man behind him picking an umbrella up off the ground. 

That evening, Markov had developed a severe fever, and four days later, he was dead. Turns out, Markov had been assassinated for his political views by the man with the umbrella, which was specifically designed to shoot a pellet laced with one of the most powerful natural toxins in the world, that's not produced by an animal - ricin. (And no, Walter White wasn't the assassin.)

"Just 500 micrograms of the stuff - that's five ten thousandths [0.0005] of what a paper clip weighs - is enough to kill a man," says Hank

But even that isn't close to the deadliest substance that Earth has managed to dish up. And the best thing is it's not produced by some complex organism that's evolved over millions of years to hunt and kill its prey with the efficiency of some kind of Freddy-Jason-The Predator super-hybrid. Nope, the most deadly substance known to science is produced by a simple, tiny species of bacterium. I'll let Hank explain to you just how potent this substance is in the episode of SciShow above, but let's just say… I'm glad I'm not a lab mouse. Because those poor bastards never even saw it coming. 

Source: SciShow