One such is nanotechnology–the ability to engineer objects at the atomic scale, to build machines whose parts are single atoms. That is the way living things are engineered: A DNA strand or an enzyme is a molecular machine. If we get good enough at working with very small objects to do it ourselves, possibilities range from microscopic cell repair machines that go through a human body fixing everything that is wrong to microscopic self-replicating creatures dedicated to turning the entire world into copies of themselves–known in nanocircles as the "gray goo" scenario.