Why does bleeding stop?
For grown-ups: the science
Platelets and a net of tiny threads plug up the cut and stop the blood.
When bleeding starts, platelets gather at the injured blood vessel and stick together to form a first plug. Then, through the blood clotting process, a protein called fibrin forms threads that trap platelets and blood cells, making the clot stronger. On the skin's surface, this can dry into a scab.
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Transcript
When you get a little scrape and blood comes out, how does it stop flowing?
When you get a cut, tiny platelets rush to that spot right away. Platelets are the ones whose job is to stop the bleeding.
A protein in your blood turns into thin threads that form a net. That net traps the blood and makes a little cover over the cut.
The cover slowly gets harder, and it can turn into a scab. It protects the cut until your body heals.
Your body has its own amazing way to stop the bleeding.