Halfway through and he sank softly down behind the trunk of a huge oak.

Either in fact or in a sort of mental illusion, he had heard a moccasin brush a dry leaf far away.

The command of Tayoga, though spoken in jest, had been so impressive that his ear was obeying it.

Firm in the belief that his own dark shadow blurred with the dark trunk, and that he was safe from the sight of a questing eye, he lay there a long time, listening.
In time, the sound, translated from fancy into fact, came again, and now he knew that it was near, perhaps not more than a hundred yards away, the rustling of a real moccasin against a real dry leaf.

Twice and thrice his ear signaled to his brain.