One theme that you could discuss is the supernatural. As you might have noted, many of Pu’s stories involve situations and circumstances that don’t exactly qualify as normal, earthly, everyday occurrences. Think about the relationships in the tales. A lot of them aren't between humans and humans: they're between humans and ghosts, spirits, or monsters.
In one of the tales, “Lotus Fragrance,” the protagonist finds himself romantically involved with both a fox-spirit and a ghost. In “The Painted Skin,” the extraordinarily beautiful woman appears to actually be an exceptionally hideous monster/ghoul.
Sometimes a story can contain multiple themes. If you wanted to discuss Pu’s tale “Talking Pupils,” you could bring up the supernatural and the uncanny. After all, it looks like talking creatures have taken up residence in Fang Dong’s eyes.
However, you might have noticed other themes in this story. One of those themes might be female empowerment or feminism. When Fang is caught gazing at the young bride, her maid throws dust in his eyes. A woman comes to the aid of another woman and punishes a man for his lecherous behavior. In a way, justice is served. The ensuing ordeal with his eyes seems to actually teach Fang a lesson. He stops his lecherous behavior and turns into a legitimately virtuous person.