So faint that at first he and Wharton failed to notice it, it now impressed itself too distinctly upon his consciousness for him to be mistaken.
It was a low, steady hum or moaning, such as the traveller hears when miles inland from the ocean.

He could not identify it, though he made several guesses, and was still speculating unsatisfactorily, when he received a startling reminder that there was a new peril at his very feet.
The first notice was a faint purring sound, as if made by a gigantic cat, accompanied by a rustling of the vegetation scarcely a dozen feet away.

He instantly grasped his rifle with both hands and was alert.
It was impossible to distinguish ordinary objects in the gloom, but suddenly two small circles glittered with a greenish light and the purring was succeeded by a low, cavernous growl.

Then it all became clear to him: a royal Bengal tiger was stealing upon the boat and was probably gathering himself for a leap at that very moment.
Had all the occupants been asleep the frightful terror would have played sad havoc with them before they could defend themselves.

As it was, it looked as if more than one fatality must follow his attack.
But for that phosphorescent gleam of the brute's eyes Jack Everson would not have been able to locate him, but the glow of the two objects defined the outlines and locality of the horrible thing as unmistakably as if the sun were overhead.