Given this little berry last night...
The Lao people eat this powerful bitter berry because when you do it makes water taste sweeter. Noy who works here said that they don't really like drinking water but know they must so they eat these and then happily drink the water :)
I think it's a pea eggplant berry. We found them in markets in Laos before. Hard to tell though as only saw a tiny part of one :).