Here is a picture of my "lokrou"(address for male teacher). He is standing in front of the whiteboard, the day I took the photo we were learning about the "killing stick". Its a squiggle that goes above a letter in Khmer writing. Khmer has lots of words from India (Pali/Sanscrit). These words are really long compared to Khmer words. So this "killing stick" gets rid of the last sound, so the word becomes shorter. (But you still write all the sounds, you just don't say the last sound. Actually the final sound in a Khmer word is not said very strongly, so this killing stick sort of knocks off two sounds in one go.)
Also , recently we learnt the word for "towel". I was interested to find out that the inside of a cows tummy has the same texture as a towel. So the word for towel in Khmer includes the word for cows tummy!