Methane gas? Drunken Lao soldiers? Clever monks? Or perhaps the fiery breath of the sacred naga, a legendary serpent-like being that populates waterways throughout Southeast Asia. Since 1983 (or for ages, depending on who you ask) the sighting of the bâng fai pá·yah·nâhk (loosely translated, 'naga fireballs') has been an annual event along the Mekong River. Sometime in the early evening, at the end of the Buddhist Rains Retreat (usually October), which coincides with the 15th waxing moon of the 11th lunar month, small reddish balls of fire shoot from the Mekong River and float 100 or so metres into the air before vanishing without a trace. Most claim the naga fireballs are soundless, but others say a hissing can be heard if you're close enough to where they emerge from the surface of the river. Most Thai and Lao see the event as a sign that resident naga are celebrating the end of the holiday.
There are many theories about the fireballs. One, which aired on a Thai exposé-style TV program, claimed that Lao soldiers taking part in festivities on the other side of the Mekong were firing their rifles into the air. (The reaction to the TV program was a storm of protest from both sides of the river.) One bizarre suggestion is that a mixture of methane gas and phosphane, trapped below the mud on the river bottom, reaches a certain temperature at exactly that time of year and is somehow forceably released. Many simply assume that some monks have found a way to make a 'miracle'. The latter was the premise behind a 2002 comedy film entitled Sip Hah Kam Deuan Sip-et (Fifteenth Waxing Moon of the Eleventh Lunar Month), released with English subtitles under the peculiar title Mekhong Full Moon Party.
Naga fireballs have become big business in Nong Khai Province, and curious Thais from across the country converge at various spots on the banks of the Mekong for the annual show. Little Phon Phisai, the locus of fireball-watching, hosts around 40,000 guests. Special buses make the return trip to Nong Khai city during the event and several hotels run their own buses, on which you'll get a guaranteed seat.
If you don't come with the right mindset, you'll likely be disappointed. The fireball experience is more than just watching a few small lights rise from the river; it's mostly about watching Thais watching a few small lights rise from the river. And even if the naga doesn't send his annual greeting on the day you come (it's sometimes delayed by a day due to the vagaries of calculating the arrival of the full moon), it'll be an interesting experience.