In the second part of the extended version of the Chinese movie Red cliff, about 1 hour into the movie, there is a long scene which shows a ceremony with rice balls: what is this ceremony?
Ok I think I have found it.
It was the Dongzhi Festival. According to wikipedia:
The origins of this festival can be traced back to the yin and yang philosophy of balance and harmony in the cosmos [...] Traditionally, the Dongzhi Festival is also a time for the family to get together. One activity that occurs during these get-togethers (especially in the southern parts of China and in Chinese communities overseas) is the making and eating of tangyuan or balls of glutinous rice, which symbolize reunion. [...] Each family member receives at least one large tangyuan in addition to several small ones.
Bold is mine.
The rice balls are called Tangyuan:
For many Chinese families in mainland China as well as overseas, tangyuan is usually eaten together with family. The round shape of the balls and the bowls where they are served, come to symbolise the family togetherness.