Creating a new symbol to reflect the deadly consequences of something completely undetectable required two essential components: the symbol had to be meaningless enough to carry zero current meaning to any culture on earth, yet had to be memorable enough for people to remember what it means. This week we go from Ancient Egypt and the pyramids to the creation of the biohazard symbol in the 20th century. Also, we learn wtf is going on with beavers and their hatred of running water.