He knew that it was of no use to fire at the head of the advancing foe, as the thickness of the skull, together with the matted hair on the forehead, rendered it impervious to a bullet.
When the bull was within a yard of him he leaped lightly to one side and it passed.

Just as it did so, Dick aimed at its heart and fired, but his knowledge of the creature's anatomy was not yet correct.

The ball entered the shoulder too high, and the bull, checking himself as well as he could in his headlong rush, turned round and made at Dick again.
The failure, coupled with the excitement, proved too much for Dick; he could not resist discharging his second barrel at the brute's head as it came on.

He might as well have fired at a brick wall.

It shook its shaggy front, and with a hideous bellow thundered forward.