I’ve been in Cambodia for over seven years now and have never heard of this annual tradition that takes place around the full moon, signaling the end of Chinese New Year. The Chinese I know who live in Phnom Penh don’t have a clue of it, and Khmers don’t want to claim it as their tradition. The most prominent community still practicing it around Phnom Penh is in Takmao (the biggest celebrations). Festival activities include a wide range of spirit mediums, channeling the gamut of intentions towards their human communities. These mediums will draw blood and use it to facilitate a prediction, guide decisions and confer protections.
Given I have little interest in seeing it, I have very scant knowledge of the event. So here’s a Cambodia Daily piece on it: Spirits, Possessions Mark End to Chinese New Year, by Dene-Hern Chen and Chin Chan, February 27, 2013