The Journey of Life as a Tree
The narrator compares the journey of life with a tree: "Futures not achieved are only branches of the past: dead branches." This illustrates that at any given point there are countless branches to follow, but the ones we do not follow will be dead to us; they may come to life for another person, though.
The Empire Like a Corpse
Kublai Khan knows that his empire is "rotting like a corpse in a swamp, whose contagion infects the crows that peck it as well as the bamboo that grows, fertilized by its humors." By using this simile, he emphasizes the decayed state of his realm, which has a destructive effect on bordering territories as well. As the corpse cannot be revived, the emperor implicitly acknowledges that the state of his empire cannot be improved.
A Cargo of Regrets
After Marco Polo reveals that he has only been describing Venice the whole time to preserve his memory of his hometown, the emperor replies, "You return from your voyages with a cargo of regrets!" This metaphor emphasizes how much Polo seems to miss Venice, and how much he thinks about missed opportunities and the decisions he made in the past.
The Emperor as a Cat
The emperor has had a feeling that Marco Polo has not told him stories about real cities. He has been suspecting that Polo is ridden by a deep feeling of nostalgia, so "for an hour he had been toying with it, like a cat with a mouse," which illustrates that he is sure he knows Polo's true intentions and will eventually get him to confess them.
Marco Polo as a Smuggler of Moods
Kublai Khan compares Marco Polo to a smuggler: "This is what I wanted to hear from you: confess what you are smuggling: moods, states of grace, elegies!" This shows that he has finally understood that Marco Polo does not tell him stories of real cities; instead, he conveys his own feelings of nostalgia.
