The mammalian circulatory system must be finely tuned to respond quickly to injury to prevent blood loss, but also specifically to avoid widespread clotting.

“If you think about it, if you're a mammal and you have a circulatory system, you have to be able to sense injury so you can keep your blood from flowing out of you. So the system has to be incredibly tuned. And you as an engineer will appreciate how you must be able to respond incredibly quickly, but it has to be specific. So you can't get clots happening.”