Nick Iwaniuk, age 8, of Youngstown, Ohio, for his question:

Are my fingernails made of livid or dead cells?

The fingernails you can see are made of dead cells    but this is only part of them. As you know, they keep on growing. If you do not trim the ends, they get longer than the tips of your fingers. The tips seem to be the growing ends of your nails    but they are not. The nails grow from roots buried in the flesh at the opposite ends. And these roots are made from very busy living cells. They keep on making the special dead cells to build the nails longer and longer. This new material grows from the roots and pushes the nails up toward the tips of your fingers.

So the nails you can see are made of dead cells and the hidden roots are made of living cells. The dead cells have no blood vessels and no nerves to feel pain. It does not hurt to trim the tips. But their sides and undersides are fixed unto the living flesh of your fingers. This flesh has lots of sensitive nerves. when you tear a nail below the tip, it damages the living cells of a finger which hurts.