If he did not identify the noise, he growled fairly softly.

But if the noise were made by a man or boy who moved softly and therefore suspiciously, Jerry learned to growl loudly; if the noise were loud and careless, then Jerry's growl was soft.
It never entered Jerry's mind to question why he was taught all this.

He merely did it because it was this latest master's desire that he should.
All this, and much more, at a cost of interminable time and patience, Nalasu taught him, and much more he taught him, increasing his vocabulary so that, at a distance, they could hold quick and sharply definite conversations.
Thus, at fifty feet away, Jerry would "Whuff!" softly the information that there was a noise he did not know; and Nalasu, with different sibilances, would hiss to him to stand still, to whuff more softly, or to keep silent, or to come to him noiselessly, or to go into the bush and investigate the source of the strange noise, or, barking loudly, to rush and attack it.
Perhaps, if from the opposite direction Nalasu's sharp ears alone caught a strange sound, he would ask Jerry if he had heard it.

And Jerry, alert to his toes to listen, by an alteration in the quantity or quality of his whuff, would tell Nalasu that he did not hear; next, that he did hear; and, perhaps finally, that it was a strange dog, or a wood-rat, or a man, or a boy--all in the softest of sounds that were scarcely more than breath-exhalations, all monosyllables, a veritable shorthand of speech.
Nalasu was a strange old man.

He lived by himself in a small grass house on the edge of the village.