A young girl had a sleepover with several of her teenage friends attending. Shortly before midnight, she told her guests that there was a grave at the edge of the woods behind her house and anyone going there on a full moon and standing too close to the grave would be pulled into the grave by the bony hand of the old man buried there.
One fifteen-year-old girl scoffed at the story, and after much teasing, accepted the challenge of going alone to the grave. As proof she had actually gone all the way she was to stick a large pitchfork into the top of the grave for inspection by all the others the next morning.
The girl left and did not return. The others got scared (and afraid to wake the adults in the house) fearful that they'd be in serious trouble. They stayed in the girl's room for hours, until they were certain they had to do something.
Early the next morning, they all huddled together and nervously made their way to the grave. There they found their friend, lying dead from exposure, beside the grave with her long night gown pinned to the grave where she had stuck the fork through it and into the hard clay covering the grave.
Credited to Alvin Schwartz