( The trance is called khong kheun which I have heard translated as both spirit possession and, more simply, loss of self-control. The belief is that the himmapant (animal spirits, minor gods) spirits embodied in the tattoos take over in times of danger (thus protecting the wearer) and, during the Wai Kru ceremony, come forth as their power is rejuvenated. )
to quote the man at the bus stop,
"When you have amulet, you can lose it. But if it is in your skin, you cannot lose it, unless by your soul. If you make wrong action, the protection fly away from you. It is like radio, if broken... you still have the radio, but no signal. When this happens, you have to take the radio to get fixed, and then it works again."
So, according to this beautiful interpretation... Wai Kru (the event on Saturday I've yet to write about) is thousands of people gathering to get their radios fixed.