15 Things You Probably Didn’t Know About Blood

Does menstrual blood really attract bears? Why does blood look blue in your veins? And why were the first blood transfusions performed with animals? Here are 15 facts, historical and biological, you probably didn’t know about blood.

Source: 15 Things You Probably Didn’t Know About Blood

The reason horseshoe crab blood is blue is the binding agent is copper, not iron. This species is thought to be the most “ancient”, having seen Jurassic dinosaurs come and go.