I've made the spicy mushroom soup "Gang-head" before, but that was in a kitchen with nice clean supermarket mushrooms. Out on the farm things get a little more rustic.
I can pick wild mushrooms from the wooded area behind the farm, but they do need some serious cleaning. You can see from the photo just how mud caked the mushroom are, being a rice farm, it's usually wet and usually muddy.
In the west they say you should gently brush the dirt of mushrooms so as not to lose the flavours. In Thailand, I'd say, wash them carefully under running water if you want to live. Better safe than sorry.
Cooking is a bit more rustic too, with charcoal being the main fuel, everything becomes a barbecue, even the soup. Since the mushrooms will produce a lot of water, I use only a little, it's enough. Soon the soup will be delicious.