In Pale Fire John Shade sees humanity as having been most "artistically caged" by mysterious powers, whereas Charles Kinbote considers that cage as being constituted by one's physical body, bourgeois morality and a person's symptomatic determinants: "With no Providence the soul must rely on the dust of its husk, on the experience gathered in the course of corporeal confinement, and cling childishly to small-town principles, local by-laws and a personality consisting mainly of the shadows of its own prison bars. Such an idea is not to be entertained one instant by the religious mind." In Nabokov's later novel, Ada, or Ardor, a bird-cage is also brought up: "Had it really happened? Are we really free? Certain caged birds, say Chinese amateurs shaking with fatman mirth, knock themselves out against the bars (and lie unconscious for a few minutes) every blessed morning, right upon awakening, in an automatic, dream-continuing, dreamlined dash — although they are, those iridescent prisoners, quite perky and docile and talkative the rest of the time."

"In 1920, Kafka's friend Gustav Janouch brought him an English book, David Garnett's Lady into Fox, which Janouch denounced as having copied the methods Kafka had invented in The Metamorphosis. Kafka immediately rejected the idea: "he did not copy that from me—it is part of our times. We both copied it. Animals are closer to us than men. Those are the bars of the cage." A week later, Kafka returned to the idea in his talks with Janouch: "each of us lives behind bars that we carry with us wherever we go. This is why there is so much writing about animals. It is an expression of the desire for a free and natural life" (Janouch 43). What Kafka wished to express through his insect and the rest of his animal menagerie was that modern life and language carried their own bars—and ones not easily pulled down. The ape of "A Report to the Academy," the beetle of "The Metamorphosis," the mice of "Josephine the Singer," the dog of "The Investigations of a Dog," and the other enigmatic creatures in Kafka's works, all express a longing for 'a free and natural life'." [...] "In his afterword to Lotita Nabokov employs this same figure of an animal (an ape) in a cage to describe the moment of inspiration that preceded his writing of that work: "The first little throb of Lolita went through me late in 1939 or early in 1940, in Paris, at a time when I was laid up with a severe attack of intercostal neuralgia. As far as I can recall, the initial shiver of inspiration was somehow prompted by a newspaper story about an ape in the Jardin des Plantes, who, after months of coaxing by a scientist, produced the first drawing ever charcoaled by an animal: this sketch showed the bars of the poor creature's cage" (Annotated Lolita 311). This article has never been found, and there is every reason to believe that Nabokov invented it for the occasion."

In Kafka's stories the animal is usually impelled forward and forced to evolve (as the caged ape in "A report to the Academy") or it must advance hopelessly toward its doom since any change of direction is equally mortiferous (cf. the cat and mouse in "A Little Fable"). All of them (not only human characters) must face a dead-end and learn that there's no way out from their present predicament. Civilized life offers no escape into freedom.

Reconsidering Kinbote's words ("...a personality consisting mainly of the shadows of its own prison bars") under the light of Kafka's little parables I began to think that Lolita's caged artistic ape and Humbert Humbert's prison bars give shape to the pedophile's tragic dimension, should we accept the hypothesis that Humbert Humbert's cage is his personality, his illness. Because they can only access HH's posthumous confessions, Lolita readers have to realize how useless it is for HH to address an imaginary jury. Like it happens with Kafka's characters, HH sits "Before the Law" and there is no one to condemn or to forgive him, while he's still living. There is no way out of his condition. There's no hope.

Perhaps we can stretch the related images of Kafka's and Nabokov's cage-bars in Lolita a little further. We may look at Pale Fire's Hazel Shade while she is standing outside the azure entrance of a bar, with its neon-barred puddles (lines 397-400). The equivocally significant words "bar/neon-bar" are 'unpoetically' placed close together (perhaps this is why while riding a bus Hazel holds onto a "stang," instead of any "bar" or post). Perhaps the word "bar" in that instance serves to emphasize the hopelessness of her romantic situation and how emprisioned she feels by her "Hazelhood." (I'm placing my trust on Kinbote's observations!).
If there's any freedom and hope left, it's up to her father to explore and to recover.