How does Jerome come to understand that Montmorency was not so angelic quite suitable for life on earth?

"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.  There is a sort of Oh-what-a-wicked-world-this-is-and-how-I-wish-I-could-do-something-to-make-it-better-and-nobler expression about Montmorency that has been known to bring the tears into the eyes of pious old ladies and gentlemen.

When first he came to live at my expense, I never thought I should be able to get him to stop long.  I used to sit down and look at him, as he sat on the rug and looked up at me, and think: “Oh, that dog will never live.  He will be snatched up to the bright skies in a chariot, that is what will happen to him.”

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.

To hang about a stable, and collect a gang of the most disreputable dogs to be found in the town, and lead them out to march round the slums to fight other disreputable dogs, is Montmorency’s idea of “life;” and so, as I before observed, he gave to the suggestion of inns, and pubs., and hotels his most emphatic approbation.