Today marks this year's Mid-Autumn Festival, which falls on the 15th day of the eighth lunar month. The traditional Chinese festival is all about the full moon and family reunion it represents. When people sit together at night and enjoy the gentle moon, an ancient poem, "Prelude to Water Melody", is often read.

The masterpiece written by Su Shi, a great writer of the Song Dynasty (960-1279), is hailed as the best poem on the Mid-Autumn. Why is it so special? What's the story behind this poem? Let's find out in the fourth episode of "Mastering Chinese Poetry."