Each year, hundreds of fireballs spontaneously explode out of Thailand’s Mekong River. Known as “bung fai paya nak” or “Naga fireballs,” they have appeared on the “late autumn night of the full moon at the end of the Buddhist Lent for as long as anyone can remember,” according to a 2002 Time magazine story about the phenomenon. Some believe the balls come from the breath of Naga, a mythical serpent that haunts the river. (Locals use old grainy pictures and postcards of the mythical beast to prove its presence to tourists.) Others believe the fireballs are actually pockets of methane bubbling up from the river, but many locals remain convinced that the fireballs are of a supernatural origin.