He was not afraid, but he felt that creepy feeling that accompanies the mysterious.  Suddenly he recollected that he had left his rifle behind when he plunged into the bushes.

He remembered this when the desire came to him to put the rabbit out of its misery.  It had been caught by the hind leg and had wrenched it out of joint in its frantic struggles to get free.  Jack made his way back to where he had left his rifle.  But when he got back to the trap ready to end the poor creature’s life, the rabbit was not there!

The trap was empty!

Then he looked about him.  The ground was covered with blood and fur as if the rabbit had been torn to pieces.

“Some animal,” was his first thought.  Then, on examining the trap, he found that the thong which had ensnared the rabbit had not been broken or torn loose as would have been the case had some wild creature pounced on the rabbit and dragged it off.

It had been untied!

Jack had just made this discovery when he noticed something fluttering from a thornbush.  He was sure it had not been there before, for he had noted the surroundings of the trap carefully.  He examined the object that had caught his attention.  It was a bit of canvas, seemingly torn from a garment made of that material.

“There is somebody else on the island!” gasped Jack, looking round with white cheeks.

He clutched his rifle firmly.  Looking about him he half expected to see some wild face peering at him out of parted bushes.  But nothing of the sort happened.  Feeling very uncomfortable, Jack came away from the place and made his way back to camp.

This time he made up his mind to confide in Zeb.  The prospector was as mystified as Jack over the events of the night and the incident of the rabbit trap.  But he was unable to throw any light on the affair.

“It might be an Indian,” he said, “or——­”

“It might be the man that built that hut and left the shovel sticking in that barren place down yonder,” said Jack.

“In that case, wouldn’t he be livin’ in ther hut instead of snoopin’ round the island?” asked Zeb.

This view seemed to be incontrovertible.  At noon the professor, who had been scouting over the island looking for specimens which might give him some clue as to the mineral deposits they had come in search of, arrived in camp breathless and indignant.

“A joke’s a joke,” he said to the boys, “but this is going too far.”

“What’s the matter, professor?” asked Dick.

“Yes, what’s happened?” asked Tom, who saw that the man of science was really angry, and for some reason blamed them for whatever had irritated him.

“As if you didn’t know,” declared the professor.  “I set my bag of specimens down on a rock while I went to investigate a peculiar-looking formation.”

“Well?” said Jack.

“Well, I heard a soft footstep and the crackling of some twigs.  I looked round and my bag of specimens had gone.  Now which of you boys played that foolish joke on me?”