“What’s that?” asked Chot in a tense whisper.
“I don’t know,” answered Rick. “Listen!”
Ruddy set up a frightened howling.
CHAPTER XX
A STRANGE CAMP
Through the air, over the heads of Rick, Chot and Ruddy, now seemingly on one side and now on the other—surrounding them, as it were—the mysterious noise came and went. Now it almost died away—an expiring groan it might be from some unseen inhabitant of the tunnel. Then again, it would fairly howl around them. And at the conclusion of one of these weird howls Ruddy again joined his voice to that of the unseen one, making so nerve-racking a combination of notes as to cause cold shivers to run down the spines of the lads.
“Whew!” whistled Chot, as the sound seemed to vanish into the mysterious black recesses of the place, “this is too much for me!”
“You’re not going to quit; are you?” cried Rick, for he saw the light of Chot’s lantern drawing away.
“Why not?” demanded Chot. “This is fierce! You aren’t going to stay; are you?”
“I’m going to stay and I’m going on!” declared Rick firmly.
“Well,” went on Chot, “I’m not going to desert, but when Ruddy howls like he did—that’s enough. There’s something unhuman here, Rick.”