There’s a rare type of blood that’s shared by only 43 people in the entire world. ‘Rhnull’ blood doesn’t contain any of the Rh antigens that 99.9% of humans have. It’s often called ‘golden blood’ because it can be given to anyone who has a rare Rh blood type, but there are only 9 active donors, so it’s only used in extreme circumstances. (, )

Lewis and Clark brought mercury chloride, a strong laxative, with them on their expedition across the US. Because the mercury it contains passes right through the system, archaeologists have been able to find their trail by locating what’s left of their makeshift latrines and testing the mercury content. More than 100 years later, their footpaths are overgrown, but their poop remains. (, , )