Then he was afraid that the Indians would by some accident, lean something against the curtain of small roots between two other big trees, and that the curtain might not be strong enough to support it, in which event their hiding-place would be discovered at once.

He was afraid, too, that some slight noise inside the fortress might catch the uncommonly quick ears of the Indians.
All these were dangers well worth considering; but now a new, and much greater danger began to show itself.

The drift was largely composed of light wood, and from his hiding-place Tom could see that the fire built by the trees had communicated itself to the hammock, and that the flames were rapidly spreading.

The danger now was that the fire would burn into the alley-way and so cut off retreat from the fortress, and if so those inside would be burned alive.

Quitting his place of observation therefore, he established himself as a sentry in the alley-way, having determined, if the fire should approach the passage, to take Joe and Judie out of the fortress and into one of the aisles near the farther edge of the drift-pile.