What is the theme of the story "A Martian Sends a Postcard Home"

As the title indicates, this poem is written from the perspective of a Martian that visits Earth. In the poem, the Martian tries to explain the phenomena it sees on Earth, such as books, toilets, and rain, all discussed in a postcard home to its planet. However, due to the Martian's unfamiliarity with these concepts, they are presented in a strange way that makes them seem exotic and puzzling. The theme is looking at how strange human nature is when looked at objectively.