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Traditionally, the Khmer people have a unique method of recording information on Tra leaf. Tra leaf books record information on legends of the Khmer people, the Ramayana, the origin of Buddhism and other prayer book series. They are greatly taken care of and wrapped in cloth as to protect from moisture and the jungle climate. Bonn Om Teuk (Festival of Boat Racing), the annual boat rowing contest, is the most attended Cambodian national festival. Held at the end of the rainy season when the Mekong river begins to sink back to its normal levels allowing the Tonle Sap River to reverse flow, approximately 10% of Cambodia's population attends this event each year to play games, give thanks to the moon, watch fireworks, and attend the boat race in a carnival-type atmosphere. Popular games include cockfighting, soccer, and kicking a sey, which is similar to a footbag. Based on the classical Indian solar calendar and Theravada Buddhism, the Cambodian New Year is a major holiday that takes place in April. Recent artistic figures include singers Sinn Sisamouth and Ros Sereysothea (and later Meng Keo Pichenda), who introduced new musical styles to the country.