When the body is injured several things happen to fix you. First, your white blood cells go to the area of injury and fight off any infection that might have got in. They also kill any weak and dying cells and remove the rubbish of already dead cells. At the same time, cells that are badly hurt might decide to kill themselves. This happens all the time anyway when a cell gets old, but cells choose to do it if they are hurt. Cells that aren’t too bad then switch on special genes which start special repair machinery to help fix some damage. All this is the first stage. Another thing that happens in the first stage is that if there is any bleeding, then platelet cells form a blood clot so you don’t bleed to death. Once all this is done and the damage is cleared away, healthy cells then start making copies of themselves to fill the gaps where other cells die. This is a really important process and the body has to watch it carefully because if it goes wrong it could mean cancer. This is one reason why smoking causes cancer. Every cigarette damages lung cells and they keep on having to heal themselves. If they do it over and over, eventually one will go wrong and start a cancerous growth. Luckily for us the body is very good at keeping an eye on this process and so cancer doesn’t usually happen.