If you have a cork piece on top of a nail, it is extremely hard to keep it stable, and the slightest action will make the cork fall off. However, when you balance it on top of a nail but put forks into it, apparently it becomes extremely easy to keep stable. I looked in my textbook and it said that this is because the center of mass is lowered from its original position (and the center of mass was below the point of contact in the first place), which is confusing because if you are adding more mass towards the top, shouldn't the center of mass move upward and not down? It also says that when you try to topple the cork with the forks in it, the center of mass moves upward, increasing its potential energy.
Can someone really good at this stuff explain the entire process to me? I am truly confused about this.