I'm familiar with Theravada Buddhism to a small degree and I spent a year in Thailand about 45 years ago. As to the merits of the movie, it tries a bit too hard to be comical. I liked the movie, Nang Nak, better. It was made 14 years earlier than this movie and follows a slightly different theme, which I like better. Looking between your legs is a common superstition in Thailand where if you do, you might see a ghost, hence the plot of the movie. Regarding their teeth being blackened, that is also common and, if done regularly (believe it or not), leads to better dental health.