Why are the pirates upset when they discover the skeleton in the woods?

They find a human skeleton lying at the foot of a tall pine tree in a perfectly straight, unnatural position, his feet pointing in one direction and his hands, raised over his head, the opposite direction. Silver believes that he man's body has been placed that way to serve as a compass, and, after checking their own compasses, they believe this to be correct. After closer examination, Silver believes that the skeleton is one of the pirates that Flint killed, someone they recognize as Allardyce. They notice that although most of the clothing has rotted away, none of the possessions that may have been in the man's pockets are lying around. The men feel haunted by the spirit of cold-blooded Captain Flint and walk closely together as they head toward the treasure.