Symbolism, Imagery, Allegory
Some see a man made of cheese, others see a rabbit. As much as we like cheese, we'll table that one for now. In Chinese folklore, a rabbit lives in the moon, pounding the elixir of life for the Moon goddess Chang'e [https://owlcation.com/social-sciences/moon-rabbit]. As Rachel gazes at the moon while she talks to Sophie Khoo, she sees that rabbit-like figure:
"Suddenly the rabbit-like figure on the moon reminded her of Nick, a little boy stuck up there in that glittering palace all by himself" (2.13.25). To her, as she learns more and more about Nick, he seems an anomaly in this world of money and glitz. She envisions him an isolated child, trapped in a world he didn't choose.
As she gets to know Sophie better, she sees that Nick isn't the only one who is down-to-earth and different from all the rest. "Rachel peered up at the moon, and this time, the rabbit boy didn't look so alone anymore" (2.3.41).
We don't see this imagery repeat elsewhere in the novel, but it helps us see how Rachel comes to understand how Nick fits into this world she never knew even existed.