There might be water-serpents hidden under those overhanging trees, waiting amongst the roots ready to seize and pull him down; or huge alligators or crocodiles might be lurking in the deepest holes.

Nic was not learned enough as to the way in which their teeth fitted between the others or into holes in the opposing jaws to know which was which.

It was enough for him to remember that they were shaped like the fierce little efts which seized the worms in ponds at home when he had been out fishing.
The thoughts were horrible, and he stood shivering, and had it been broad daylight his skin would have been seen becoming covered with tiny pimples, like the cuticle of the goose plucked, and assuming a reddish, purply hue.
"Oh," he thought, "if I could only escape this bitter task!" But he was too determined to attempt that, though he could not help putting off the task as long as he could; for cold water which looks bad enough at dawn in a bath in a comfortable dressing-room seems far worse on the banks of a river; and a hundred times worse when an active brain suggests the possibility of its containing fierce, hungry reptiles in all their amphibious horror, watching and waiting, in a land of blacks, for a tender, well-fed breakfast off a delicate, well-bred white.
"It's of no use," thought Nic.

"I must summon up courage and do it.
He'll be waiting breakfast for me, and--Ugh! how cold!" Nic involuntarily turned his head to gaze in the direction of the trees where the fire was blazing, uttered a faint cry of surprise and horror, and turned and dived off the bank into the hole, to feel quite an electric shock run through him, while the water thundered in his ears, and he formed a graceful arch in the depths.
Out popped his head directly, yards away from where he had taken his header, and he began to swim with a calm, vigorous stroke right away for the middle, gazing sideways the while and muttering to himself as he saw that the object which had startled him, shamefaced, into seeking the protection of the water, had walked close to the edge, taken up his favourite, crane-like attitude, and was watching him swim, with his lips drawn from his teeth and displaying them in a broad grin.
It was something after the fashion of a conjuring trick.

One moment a white figure had stood there in the dawning day; the next there was a loud splash, the white figure had disappeared, and a black one stood in its place, not in the least ashamed, though almost as nude as Nic.