Though he had pulled the trigger only once a series of sudden explosions followed, seemingly coming from beneath the tent itself.
"What's that!" demanded the Professor, lowering his own weapon, plainly puzzled.
"Guess the bear's shooting at us," suggested Chunky wisely.
"No. I know what it is," cried Tad.
"You know?" demanded Ned.
"Sure. It's our cartridges exploding. The fire from the lantern has got at those pasteboard boxes in which we carried the shells."
Now they were popping with great rapidity, and instinctively the boys drew further away from the danger zone, though the Professor told them the bullets could not hurt them, there being not sufficient force behind to carry them that distance.
The Professor stood his ground as an object lesson and again resumed his target practice. The tough canvas resisted the bear's efforts, and the fire was burning slowly. However, the tent seemed to be ruined and the boys feared their rifles would share a similar fate.
"He's breaking out!" yelled Chunky, who was some distance to the right of the others, now dancing up and down in his excitement. "Look out for him!"
With a last desperate effort, the animal had succeeded in forcing his way through the stubborn canvas.