Watermelon and apple are round.
People who are reunited are happy.
It is painful to be divided into flesh and blood.
People who miss their loved ones
Look at the bright moon in the sky
Who can swallow moon cakes?
Metaphor can also be used as simile. Round objects such as watermelons and apples are used to symbolize the bright moon and moon cakes representing reunion.
Watermelon and apple are round, and round can remind people of reunion.
The author misses his hometown and relatives. Any round object in his life can evoke the author's homesickness and express his deep thoughts and attachment to his relatives in his hometown.