Snarl the dog has been scolded, and the poem is his defence. He did his job, he insists, and then, with a politeness that is itself a kind of trick, he redefines what the job was. By the end, the master who told him off looks like the one who needs guarding.
The first six lines set up the case in a narrator's voice. Snarl guarded the door impartially, "spar'd nor Rich nor Poor", and barked even at "pretended Friends". His reproof, "better Fed than Taught", suggests a pampered animal with poor manners. When he speaks, the fable turns into a courtroom. His vocabulary is legal: "Charge", "Commission", "Delinquents", "testify". He calls his master "your Worship" and argues that nobody ever told him the task was "confin'd" to beggars. That legal tone is a nice irony, because lawyers will soon be among his targets.
The first half of his speech deals with the easy cases. The beggars who "shrink an Arm, or prop an able Knee, / Or turn up Eyes, till they're not seen, nor see" are neatly caught in that last line, where the tangle of "seen" and "see" imitates the faked blindness. Thieves come off almost respectably, since they "fairly stake their Necks against your Wealth". That gambling metaphor makes a burglar sound like a man who at least knows the odds. Whips and Tyburn, London's place of public hanging, await him. These offenders are "known", and the law already handles them. Catching them takes no special talent.
Then comes "But since", and the poem changes direction. Nature has lent Snarl "An exquisite Discerning by the Scent", and smell becomes a moral sense that picks out what eyes and laws miss. The list that follows is driven by tracking verbs: "I trace", "I grudging note", "I mark". The flatterer "fawns", which is a dog's behaviour given to a human, so the real dog is the honest one. The "rallying Wit" both "commends and jeers", praise and mockery in one breath. The parasite's praise for "the good Bits" is paid for by the food that will "oil his Throat", an unpleasantly greasy image. The lady "you so fondly toast" brings the master himself into the frame. She "plays your Gold, when all her own is lost", which echoes the burglars' gambling but with a difference: the thief risks his own neck, and she risks your money. The lawyer who "fences your Estate by Law / Yet still reserves an undermining Flaw" works as a pun. A fence protects, but this one is built with a gap left in it.
Formally, the poem is written in rhyming couplets of ten syllables, a measured and orderly form that suits an argument. Most couplets close firmly, and the rhymes often snap shut on a judgement, as in "Wealth/Stealth" or "Law/Flaw". The sentence about the dog's gift runs across a line ("by Nature lent / An exquisite Discerning"), and the longer, looser flow suits a speaker warming to his own talents. The capitalised nouns and the polished couplets suggest a poem of the late seventeenth or early eighteenth century, though that is an inference from the printing and style, not a fact I can confirm. The final couplet rhymes "tell" with "Smell". It ends on the body, with a comic drop from moral insight to a twitching nose. The verbs "Provoke" and "offend" work on two levels at once, since the dog is offended in conscience and in nostril.
The poem is significant because the fable lets a humble speaker say uncomfortable things. Snarl never raises his voice against his master. He defers, he explains, and he leaves the verdict to the reader. Yet his argument moves the danger away from the poor at the gate and toward the charming people already seated at the table. The master gets no reply, so the question of who judges character better, the man or the dog, stays open. Snarl's only "Fault" may be that he is right.