If a person gets a cut on their body, that person may bleed. To stop the bleeding, the human body does several things. First, the brain orders the liver to produce chemicals that will help the clot to form. When the chemicals released by the liver arrive at the injury, the coagulation begins. In the mean time, the brain also lessens the blood flow near the injury (by tightening the veins and arteries in that area), so that not as much blood is lost. 