Healing cut. Image 2 of 3. Healing cut on a man's finger ten minutes after the injury. The blood has started to thicken and clot. Clotting occurs as platelet cells in the blood encounter a damaged blood vessel wall. This causes them to release chemicals which cause the protein Ifibrin i to be produced. This entangles red blood cells, leading to clot formation. Clots seal the injured site, preventing blood loss and stopping bacteria and other pathogens from entering the body. For a sequence showing this cut as the blood clots, see images M330/868-870.