For most humans, the ability to clot blood is vital—if not, even a small cut could mean bleeding to death. Simply put, blood clotting (or thrombus) is actually a mass of protein fibers that trap lymph and red blood cells, eventually hardening into a cap—what we call a scab—that protects the damaged area. The clotting reaction is thought to be platelets in the area of a cut releasing chemicals into the bloodstream, starting the formation of a clot through a series of enzyme-controlled reactions.