He might as well have fired at the boiler of a steam-engine.

The entire body of an alligator--back and belly, head and tail--is so completely covered with thick hard scales, that shot has no effect on it; and even a bullet cannot pierce its coat of mail, except in one or two vulnerable places.

Nevertheless the shot had been fired so close to it that the animal was stunned, and rolled over on its back in the water.

Seeing this, the old trader rushed in up to his chin, and caught it by the tail; but at the same moment the monster recovered, and, turning round, displayed its terrific rows of teeth.

The old man uttered a dreadful roar, and struggled to the land as fast as he could; while the alligator, equally frightened, no doubt, gave a magnificent flourish and splash with its tail, and dived to the bottom of the river.
The travellers returned disgusted to their canoe, and resumed their journey up the Amazon in silence.
The vulnerable places about an alligator are the soft parts under the throat and the joints of the legs.