On my hand are five digits.  Each finger is a different length.  Each has a joint at the base of my hand and two more before it reaches the tip.  But hiding on my hand is the imposter!  On one end lives a thumb. (He only has one other joint.)  But he doesn’t bother the other fingers and is very willing to help out whenever he can; so the fingers accept him and don’t put up a fuss when someone says, ‘hold up five fingers.’  Each finger has a hard nail protruding from it.  You’d think this would hurt – a tough slab of dead material mercilessly ripping its way through soft flesh, never ceasing but continuing on day after day until the end of is has to be hacked off to keep it under control – but it doesn’t.

The top of my hand is covered with small hairs.  The bottom of my hand is completely bald.  The top of my hand has freckles and moles.  The bottom of my hand is blemishless.  Why is it that the top of my hand has fingernails but the bottom does not?