ME: WHAT IS THE MOST TOXIC THING IN THE WORLD? GOOGLE: BOTULINUM TOXIN BOTULINUM TOXIN IS CONSIDERED THE MOST TOXIC CHEMICAL, BASED ON THE FACT THAT A VERY SMALL AMOUNT OF IT—A NANOGRAM QUANTITY—WILL KILL A HUMAN BEING. IT'S A NATURALLY OCCURRING CHEMICAL, MADE BY A BACTERIA (CLOSTRIDIUM BOTULINUM).