In the left circle, can be seen a rabbit. In the right circle, are two fish as each might appear on a fishing line. The boy, it would seem, is thinking about rabbits and fish. There is a battle scene (men with spears) to the left of the rabbit, which is similar to some of Allston's drawings.
At age 10, Winslow Homer was including illusions that then could allude to ideas salient to the subject of the artwork. This was 1846, three years after Allston died, but four years before Lectures on Art was published after editing by Richard Henry Dana Jr. Homer was following Allston's methodology. There were lots of possible sources. His artist/mother, Henrietta Benson Homer, Richard Dana, Jr., or others in the community familiar with Allston's ideas.