Sometimes, People Become Skeletons
Sometimes the dead became ghosts, but sometimes they became skeletons. It all depends.
The angry become ghosts.
They throw thing across the house and slam doors in your face and rattle windows until you scream for cover. It makes them feel better when you scream. They'd rather hear you scream than hear themselves scream about whatever still sparks their anger. In the end, the angry ghosts refuse to go because they're not done being angry.
Those who are mournful become ghosts.
They make terrible moaning sounds that will chill your neck. They linger in graveyards or around corners and send frigid gusts of air through hallways, making the hair on your arms rise. These mournful ghosts never recovered from something, or someone, being taken from them. They carry on, waiting for that thing to come back. It never does.
Ghosts are also what become of people who have things unfinished to do.
They bounce through houses bumping against doors and windows, rattling them, knocking into picture frames and skewing them sideways. These ghosts don't know what to do with themselves. You want to feel sorry for these lost ghosts, but sometimes they'll become so frustrated they throw things or wail uncontrollably, sending house cats running into the next room. Then it's harder to feel sorry for the ghosts because they just knocked the lamp off the table and broke it again.
Sometimes, the ghosts remember what they had to do that was unfinished. They may sing about it. Or talk to you about it in a windy, whispering voice. But many don't remember, and bounce about the house directionless.
Those are the reasons people become ghosts when they die. Otherwise, they usually can move on.
But sometimes, when people die, they're just so, so empty.
They're laid down in the ground and for a long time, their bodies will lie still. But when the skin has fallen away and the muscles have gone and when even the fingernails and hair have shriveled, the old bones remember how empty their soul once was. And then, there's nothing left to fill up the bones. No organs or brains or heart. And the old bones get up out of the ground and start walking to try and find something to fill them up again.
On some particularly dark nights, when nothing but the stars throw light below, you can see the skeletons clambering out of the graveyards, toward the street. Their knees clack together and the collarbone shifts sideways and the teeth clatter like they're trying to say something, anything. The skeletons may reach a naked hand to you, feeling the fullness and life within you, but when you run away, they'll be too slow and tired and empty to follow. They don't have muscles, so of course, cannot run.
But long after you've run away screaming and after you've told yourself the darkness was playing tricks on you, the skeletons will still wander the dark streets, looking for something they lost in life and which they'll surely never find now in death.