A lone cell exists on a sky blue backdrop. It wiggles around going nowhere in particular. You nudge it towards other cells that have come into view. They bond together and are now one organism with multiple cells. Now that you have a base organism. It starts to multiply and grow. You nudge them around in order to make a more cohesive shape. Everything is going great, except for one cell. It looks a bit sickly. Better get rid of it. It's definitely diseased. You forcefully nudge the other cells away from it in attempt to break the bonds. It works, the diseased cell is now separated from the rest of the organism. You pull the rest of the healthy cells away from the diseased cell. Everything is fine, except for the fact that the diseased cell has now started to multiply. It looks like the diseased group of cells want to attempt to rejoin the healthy mass. The battle has begun.