Imagine yourself going through a Halloween haunted house with some kids, when all of a sudden the Mad Scientist wants one of us to volunteer to lie down on a bed of nails. A bed of nails! They claim it's a science demonstration, but it looks more like a torture device to you.
The funny thing is, this one girl pops up to try it out, and she didn't seem harmed at all. Then a boy tries it. Pretty soon everybody tests the bed of nails, and no one gets hurt. What's going on?
A bed of nails sounds terrible and it looks even worse, but I hadn't counted on how weight is distributed. Think of it this way. You can press your fingertip lightly on a nail without it hurting. If you put the other end of the nail on a scale and then press, you can see how many pounds of pressure you can put on one nail without it hurting you. Don't press too hard!
Suppose the answer is one pound. You can press down on a nail until the scale reads one pound, and beyond that you don't want to press any harder. Okay, one pound of pressure per nail is safe for you. So, if you weigh 200 pounds, you can lie on a bed with at least 200 nails on it and not be hurt. That's because each nail is supporting only one pound and your weight is evenly distributed.