This is what I learned as a child:

You best not laugh when the hearse goes by
for you may be the next to die
they'll wrap you up in bloody sheets
and then they bury you bout 6ft.
things go swell for about a week
and then your casket begins to leak
the worms crawl in the worms crawl out
the worms play pinochle on your snout
(SPEAKING)
YOUR EYES THEY TURN A GHASTLY GREEN
AND PUS COMES OUT LIKE WHIPPING CREAM
(sing again)
and I forgot my spoon but I got a straw