It is a mystery which has confused millions around the world. Several fireballs appear along the Mekong river in Thailand each year as people gather to witness it.
Interestingly, it is not just a one-off event, the fireballs typically are many and some witnesses say even thousands can be seen. Locals call it the mythical 'Phaya Nak', a giant serpent which appears in the sky from inside the river.
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