The first thing I learned in first aid was the seriousness of bleeding. After a major accident it's the biggest risk to a person's life.
Scientists have invented tiny 'clotting balls' that can be injected to help the body's clotting system stop bleeding much more quickly.
They've only tried it in mice so far, but they plan to test it on bigger animals next, and then on humans. It could make a real difference to the number of people who survive traumatic accidents, or even on the battlefield.