It seems a rock is indeed a multi tool (as recently mentioned in another thread). You can hunt with it, hammer with it, squash things, stop cars from rolling away, make sparks (if it is the right kind of rock), stop things blowing away, cut with it (again, if it is the right kind of rock and chipped just right), build walls, drown unwanted humans with it (and stop the body from inconveniently floating back to the surface), the list is probably near endless .......