First observe this paragraph 4-7-7: "That, in some Fields of his Country, there are certain SHINING STONES of several Colours, whereof the YAHOOS are violently fond; and when Part of these STONES are fixed in the Earth, as it sometimes happeneth, they will dig with all their Claws for whole Days to get them out, and carry them away, and hide them by Heaps in their Kennels; but still looking round with great Caution, for Fear their Comrades should find out their Treasure. My Master said, he could never discover the Reason of this unnatural Appetite, or how these STONES could be of any Use to a YAHOO; but now he believed it might proceed from the same Principle of AVARICE, which I had ascribed to Mankind. That he had once, by way of Experiment, privately removed a Heap of these STONES from the Place where one of his YAHOOS had burried it: Whereupon, the sordid Animal missing his Treasure, by his loud lamenting brought the whole Herd to the Place, there miserably howled, then fell to biting and tearing the rest; began to pine away, would neither eat or sleep, nor work, till he [the Master] order a Servant privately to convey the STONES into the same whole, and hide them as before; when when his YAHOO had found, he presently recovered his Spirits and good Humour; but took [better] Care to remove them to a better hiding Place; and hath since been a very serviceable Brute."

Here is my interpretation of the last half of the passage: The Yahoo finds his stones missing, thinks he has been unmindful about protecting them better (as evidenced by "took Care to remove them to a better hiding Place"), loses his self-control, then pines away (conceivably into a state of mental depression/forgetfulness). Then he later finds the stones, decides to take better care of his Stones (i.e., "be more mindful"). He eventually forgets his past slight and becomes a "serviceable Brute".

Now consider these English words:
--FORGET: "be neglectful or unmindful of something;
--FORGETFUL: "marked by neglectful awareness or thoughtless in attention."
--FORGET ONESELF: "to lose one's control or self-restraint".
--OBLIVIOUS: "lacking concious awareness, unmindful of something, (sometimes of a past slight)".

Now we come to the Greek word LE*THOS, which means "forgetfulness, place of oblivion". To see how this wordplay works, take a blank piece of paper and write on it, in order horizontally, the following Greek letters that make up LE*THOS:

LAMBDA: lower-case form only
E*TA: upper-case only
THETA: preferably upper-case for sake of uniformity; this represents one letter, TH.
OMICRON: upper- or lower-case.
SIGMA: lower-case only, using the one that looks like an s.

Now, turn the page over and show it to a mirror. You'll get something like this: yHO-OS.

So what do the SHINING STONES have to do with LE*THOS? Cf. Greek LITHOS, "stone", which can be precious, special and glassy [="shining"?]. Also of relevance is old Greek LATHOS, "escape from detection", as shown by the hiding of the stones. So he hid the stones but was neglectful.

LE*THOS also means "oblivion" and is related to LE*THE, the waters of Forgetfulness in Hades. Lethe is also humanistic: "Lethe as a person is as old as Hesiod. She is bad from the beginning: 'Next hateful Strife gave birth to grievous Toil, Forgetfulness and Famine, tearful Woes, Contests and Slaughters'" (Harrison). And in various descriptions, Yahoos are menial, almost mindless, laborers and brutes who are serviceable, i.e., "ready to do service; subservient; capable of being applied to a proper function or purpose."

There is another wordplay present. Near the end of the passage, Gulliver writes, "he presently recovered his Spirits and good Humour". We can safely assume that the YAHOO rejoiced. A Greek-English Lexicon lists, but does not define, the word GE*THOS. An official source tells me that it means "happiness, exultation, rejoicing, delight."
The point of all this is that GE*THOS, when written in Greek orthography, looks like this: yHO-OS, without any juggling.

AVARICE: This is more of Swift's love of wordplay. In keeping with the theme of using the shapes of Greek letters, let us convert this word to Greek:

A=A, the letter alpha
v=n, the letter nu
A=A, alpha
r=g; r looks like the upper-case form of gamma
u=m/mu. I am using the letter u because I could not duplicate the similar-looking, lower-case form of letter mu
A=A, alpha
s=s, lower-case form of the letter sigma

What we have is "avaruas", which can be divided into two Greek words thus:

Gr. a, a prefix meaning "without, lack of, absence of"; Gr. varuas (transliteration=NAGMAS), a form of a word which A Greek-English Lexicon defines verbatim as "'anything piled up', as a stone wall".

Another wordplay on AVARICE takes this form: AVArEs (alpha, nu, alpha, upper-case gamma, epsilon, sigma). It means "wretch", which Oxford English Dictionary defines as "one who is sunk in deep distress, sorrow, or misfortune; a miserable unhappy person". In short, if you add avaruas and avarEs, you find that the Yahoo was a wretched creature without piles of stones.

STONES: Cf. old Greek sToNos, "moaning, groaning". He was moaning about his stones!

If you put all the various elements together as I presented them to you, you will have the basic plot of the paragraph.

Here, the word YAHOO does not refer to the people/tribe known as Yahoos themselves. What I propose is that the word is the Estonian word JAHU, which is pronounced something close to "ya-hoo" or "yuh-hoo", according to various Estonian sources. Its definition is "meal", as in oatmeal, corn-meal or flour-meal. But here Swift has perverted the intended usage of the Estonian word to refer to food in general. My interpretation of Swift's intent is not that far-fetched since the major theme of the whole chapter deals with food, a subject also dealt with in other chapters.

There is another aspect of Estonian JAHU:
In 4-7-17, Swift writes, "My Master likwise mentioned another Quality, which his Servants had discovered in several YAHOOS, and to him was wholly unaccountable. He said, a Fancy sometimes would take a YAHOO, to retire into a Corner, to lie down and howl and groan, and spurn away all those that came near him, although he were young and fat, and wanted neither Food nor Water; nor did the Servants imagine what could possibly ail him. And the only remedy they found was to set him to hard Work, after which he would infallibly come to himself."
Toomas Molder of Estonia e-mailed me this letter: "I'm not professianal language specialist but I can agree, that 'jahu' is 'nonsensical talk or discussion', 'discussion with not clear result'." Another linguist agrees basically, but adds that more often you may hear expressions with the verb JAHUMA: A"RA JAHU, "don't talk rubbish"; MIS TA JAHUB, "what is he blithering?" Trouble is, this seems to be a slang term that is not more than 100 years old. Gulliver's Travels was written in 1726. Maybe the term came from some other language... More research is needed.