I first came across this in a book...

A woman in the graveyard sat,
Oooooo
Very shoot and very fat.
Oooooo
She saw three corpses carried in
Oooooo
Very tall and very thin.
Oooooo
To the corpses the woman said,
Oooooo
"Will I be like you when I am dead?"
Oooooo
To the woman the corpses said,
Oooooo
"You will be like us when you are dead."
Oooooo
To the corpses the woman said,
"EEEEEEEEEEEEEEEEK!"

I always thought she screamed because the corpses spoke. But during my search for the poem, I realized that she's supposed to scream because she realizes her own mortality. It's a deep meaning that many of the versions seem to have lost.

And after reading various versions in this thread, I developed my own version which, in my mind, has the most important elements:
- a woman visiting a church/graveyard (I think the fact she is going to church is significant, because even though this implies she's "good" she'll still end up this way)
- the woman seeing a corpse in some sort of gruesome condition
- the woman asking if she'll be like that when she's dead, and receiving the reply of "yes."
- the woman screaming at the answer.

The only key part it's missing is the woman being skin and bones, which gives the poem its name... but I left it out for the description of the corpses.

Throw in the "ooooo"s wherever it feels natural.

A woman in a graveyard sat
Fresh out of church in her Sunday hat

She saw three corpses carried in
Nothing but bones and rotting skin

To the corpses the woman said,
"Will I be like you when I am dead?"

To the woman the corpses said,
"You will be like us when you are dead."

To the corpses the woman said,
"EEEEEEEEEEEEEEEEAAAAAAAAAAHHH!" [or something to that effect]