1. In cell cultures, normal cells divide until they form a single, continuous layer of cells, then stop.
2. If we scrap a "wound" in this monolayer of normal cells, cells from the edge move into the open space and divide until the wound is filled
3. Normal cells stop dividing when they come into contact with other cells
4. Cancer cells do not self regulate in this way Instead they conintue to divide even after they come into contact with other cells, piling up on top of one another