"Come on.

I fancy there must be a rocky shore farther on, as it's so shallow here, and it's all sand under foot." "Not all: I've put my feet on rock several times," whispered Mike.
"Well, that doesn't matter.

There's plenty of sand.

Look out!" There was a tremendous splashing in front, and the water came surging by them, while they noticed now that the sides of the place were once more closing in as they advanced.
"Shall we go back ?" said Vince; for the sudden disturbance in front, evidently the action of large animals, or fish, had acted as a check to him as well as his companion.
Mike was silent for a few moments.

Then he said hoarsely: "I'll stick to you, Cinder, and do what you do." "Then come on," said the boy, who felt a little ashamed of his feeling of dread.
"Can't be sharks, can it ?" whispered Mike, as, in addition to the lapping and sucking noises made by the water, there was a peculiar rustling and panting.
"Sharks, in a cave like this?
No.