He went near to them and threatened their bare backs with the slack of the rope.
Gingerly and shiveringly they stepped into the cold water, while the driver stood on the bank.

The water was up to their waists and he had to threaten them again with his rope before they would duck their heads under.
When he allowed them on shore again they needed no urging, it was evident, to make them hit up a good rate of speed, and back and forth along the bank they sprinted.

But the cold bath had not improved their temper, for suddenly one of them leaped and kicked sidewise at the other, with the result that both toppled to the ground.

The stout man was upon them in an instant, hazing them with the rope end.

He drove them, still lashing out at each other with their bare feet, into the water again, and after a more prolonged ducking whipped them, at a plunging gallop, upon the Annabel Lee, where they disappeared from Cleggett's view.
While Cleggett was still wondering what significance could underlie this unusual form of matutinal exercise, Dr.Farnsworth came out of the forecastle and beckoned to him.