How did Montmorency look and behave much to the discomfort of the author?

Montmorency looked like an angel and acted like a little a little terror.

To look at Montmorency you would imagine that he was an angel sent upon the earth, for some reason withheld from mankind, in the shape of a small fox-terrier. 

But, when I had paid for about a dozen chickens that he had killed; and had dragged him, growling and kicking, by the scruff of his neck, out of a hundred and fourteen street fights; and had had a dead cat brought round for my inspection by an irate female, who called me a murderer; and had been summoned by the man next door but one for having a ferocious dog at large, that had kept him pinned up in his own tool-shed, afraid to venture his nose outside the door for over two hours on a cold night; and had learned that the gardener, unknown to myself, had won thirty shillings by backing him to kill rats against time, then I began to think that maybe they’d let him remain on earth for a bit longer, after all.