A.Sklyarenko:"Updike's Chiron (I've read it 23 years ago) is mentioned in Ada (1.21): emphatic Miss Vertograd had noticed that she and giggling Verger... shared also a spectacular skin disease that had been portrayed recently by a famous American novelist in his Chiron. Vivian Darkbloom ('Notes to Ada'): Chiron: doctor among centaurs: an allusion to Updike's best novel.[   ] Since human brain resembles a walnut, this quote seems relevant: the human brain can become the best torture house of all those it has invented, established and used in millions of years, in millions of lands, on millions of howling creatures. (Ada, 1.3)

Jansy Mello: Thanks, AS for the tip about the reference to Updike's Chiron in ADA, and the leap that leads one from the horse to the bull (Taurus)
Wikipedia: "The Greek word kentauros is generally regarded as of obscure origin The etymology from ken – tauros, "piercing bull-stickers" was a uhemerist suggestion in Palaephatus' rationalizing text on Greek mythology, On Incredible Tales (Περὶ ἀπίστων): mounted archers from a village called Nephele eliminating a herd of bulls that were the scourge of Ixion's kingdom.[19] Another possible related etymology can be "bull-slayer".[20] Some[who?] say that the Greeks took the constellation of Centaurus, and also its name "piercing bull", fromMesopotamia, where it symbolized the god Baal who represents rain and fertility, fighting with and piercing with his horns the demon Motwho represents the summer drought. In Greece, the constellation of Centaurus was noted by Eudoxus of Cnidus in the fourth century BC and by Aratus in the third century"
 
In your next posting, you mentioned that: "Pushkin called Peter I velikiy Pyotr (Peter the Great). Ot velikogo do smeshnogo tol'ko odin shag (it is only a step from the sublime to the ridiculous)." This proverb is quoted by Lev Kassil in his memoir essay on Mayakovski (Na kapitanskom mostike, On the Captain's Bridge, 1934):"
Nabokov must have been aware of Pushkin's opinion about Peter I and, perhaps, even of Sigmund Freud's familiarity with the same sentence quoted in one of his examples about dream interpretation.*
 
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* - Sigmund Freud (1856–1939).  A General Introduction to Psychoanalysis.  1920.Part Two: The Dream - VII. Manifest Dream Content and Latent Dream Thought [www.bartleby.com/283/7.html -]
A sceptical patient has a longer dream, in which certain people happen to tell her about my book concerning laughter and praise it highly. Then something is mentioned about a certain“‘canal,’ perhaps another book in which ‘canal’ occurs, or something else with the word ‘canal’ … she doesn’t know … it is all confused.”    
Now you will be inclined to think that the element “canal” will evade interpretation because it is so vague. You are right as to the supposed difficulty, but it is not difficult because it is vague, but rather it is vague for a different reason, the same reason which also makes the interpretation difficult. The dreamer can think of nothing concerning the word canal, I naturally can think of nothing. A little while later, as a matter of fact on the next day, she tells me that something occurred to her that may perhaps be related to it, a joke that she has heard. On a ship between Dover and Calais a well-known author is conversing with an Englishman, who quoted the following proverb in a certain connection: “Du sublime au ridicule, il n’y a qu’un pas.” The author answers, “Oui, le pas de Calais,”  with which he wishes to say that he finds France sublime and England ridiculous. But the “Pas de Calais” is really a canal, namely, the English Channel. Do I think that this idea has anything to do with the dream? Certainly, I believe that it really gives the solution to the puzzling dream fragments. Or can you doubt that this joke was already present in the dream, as the unconscious factor of the element, “canal.” Can you take it for granted that it was subsequently added to it? The idea testifies to the scepticism which is concealed behind her obtrusive admiration, and the resistance is probably the common reason for both phenomena, for the fact that the idea came so hesitatingly and that the decisive element of the dream turned out to be so vague. Kindly observe at this point the relation of the dream element to its unconscious factor. It is like a small part of the unconscious, like an allusion to it; through its isolation it became quite unintelligible.

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