The scene shifts to a cave in Wales, where Belarius, a banished Lord, is out hunting with his adopted sons. These are, in fact, Cymbeline's lost sons, Guiderius and Arviragus, though they are going under the names of Polydore and Cadwal.
Belarius contrasts the pride and vanity of the court with the poorer but "nobler" (line 22) life they have had to adopt. The humble beetle, he says, lives safer than the grand eagle. At the court, people are reliant on others for approval and live in debt to their tailors. Guiderius points out that while Belarius has the luxury of comparing the two lifestyles, he and his brother do not, since they have never been away from this place. To them, the cave is merely a "cell of ignorance" (line 33) and a prison. Arviragus adds that unlike Belarius, they will have no tales to tell when they grow as old as him: they have seen nothing, and are like foxes or wolves, concerned only with hunting their next meal. The only courage they need is to "chase what flies" (line 42), a cowardly sort of valor.
Belarius tells them that there is nothing to be desired in the life of the court, where a climb to the peak of favor will be followed by a fall into disgrace, and where the fear of falling is as bad as the fact. Honorable acts are often punished, and what is worse, you must bow ("court'sey") in thanks for such treatment. He himself was once loved by Cymbeline, but overnight, he lost favor after being slandered by two false villains. They told Cymbeline he was collaborating with the Romans, and he was banished.
He promises his adopted sons that the first to hit a deer shall be lord of the feast and that the others will serve him. And, he says, he will fear no poison, which is an occupational hazard at court.
After the boys leave, Belarius muses how difficult it is to hide "the sparks of Nature" (line 79) inherent in the sons of a king. This is in spite of the fact that they have not been told of their royal birth (believing that they are Belarius's sons), and that Cymbeline is unaware that they are alive. When Belarius tells Guiderius, heir to Cymbeline, of his warlike feats, the boy acts out his words and "The princely blood flows in his cheek" (line 93).
Belarius, who goes under the name of Morgan, says that Cymbeline banished him unjustly. In revenge, he stole the royal children in order to deprive the king of his heirs, just as he had been deprived of his lands. But now, "the game is up," by which he probably means that the pretence cannot be kept up any longer.
Belarius contrasts the low door of his cave, where his exiled family must bow their heads as if to worship the heavens, with the high gates of monarchs, where giants can strut through, keeping their turbans on. He is symbolically making the point that the court is a place of pride, whereas they have learned humility. But paradoxically, their life is nobler than a court life, which is marked by dependence, debt and vanity.
However, this scene offers a twist on the conventional view of country life offered by Romance plays. It may be more innocent and less corrupt than court life, but to Guiderius and Arviragus, it is as limiting as a prison and as bestial as the existence of a wolf or a fox.
In comparing himself and his brother to baby birds who have never flown the nest (lines 26-7), Guiderius continues the imagery of birds that permeates the play. Posthumus is represented as an eagle in Act 1, scene 2; and Iachimo, in Act 1, scene 7, calls Imogen "alone th' Arabian bird," a reference to the legendary Phoenix. The Phoenix is said to have risen from its own ashes, out of the fire which burned at the top of the sacred Persea Tree at Heliopolis. It was a symbol of the rising sun and of the dead Sun-god, Osiris, from whom it sprang, and to whom it was sacred. The image foreshadows Imogen's later 'rebirth' from her seeming death.
Belarius's story of how he fell from favor as a result of slanders echoes Imogen's fall from Posthumus's favor as a result of Iachimo's lies, as well as Posthumus's fall from Cymbeline's favor after he married Imogen.
The scene illustrates the belief, prevalent in Shakespeare's time, that royal blood cannot be hidden, but will show itself through an inherent nobility of thought and action. Though the roof of his cave is low, the boys' thoughts "do hit / The roofs of palaces" (line 83), and they enter into Belarius's war stories in "princely" fashion (line 93).
Cymbeline: Novel Summary: Act 3 Scene 3