This has been mentioned before but not in full. It's sung on just 3 notes, repeated, viz abcb abcb, etc

(sing in a deadpan 'ghostly' voice)
A lady stood at the churchyard door oo-oo-oo-oo aa-aa-aa-aa
Where 2 women had stood before , oo etc

She saw three corpses carried in oo etc (same every verse)
Two were fat and one were thin

The worms crawled in the and worms crawled out
They crawled in thin and they crawled out stout

The worms crawled out and the worms crawled in
All were fat and none were thin

(drop voice to barely audible)
The lady to the corpses said
Will I be like you when I'm dead?

The corpses to the lady said....YES!

That usually scares the audience. Puts the willies up me.

Gwilym