For Billy, the birds that the Minpins ride symbolize pure freedom, and he is entranced by this lifestyle because his own life has very little freedom. The first few chapters show Billy gazing at the forbidden world beyond his front yard, and his boredom and frustration are evident in the fact that his mother refuses to let him venture beyond the garden alone. His keen inner desire to seek adventure is therefore realized when he gains the opportunity to soar through the air on a swan just as the Minpins ride smaller birds. While his defeat of the Gruncher is central to the novel, his true inner development occurs when Swan takes him on many secret nighttime rides to hidden and fantastical places that his closed-minded mother could never imagine. During these times, he is free to explore and see the world without any boundaries.

One of the most prominent symbols of the novel is the Forest of Sin, which represents the temptations and hidden dangers of the unknown. Billy’s mother focuses on the dangerous aspect of the forest, while the Devil emphasizes its hidden delights by promising Billy a forest full of ripe strawberries.