From - Andrew Zeylemaker
I like to call this sound Psycho. Mute all strings and strum behind the nut hard and fast in a downward motion using a straight crotchet rhythm - this makes a dissonant sound which my friends and I consider to be close to the strings sound used in the shower scene from the movie Psycho . This sound comes in handy when you are at a jam and someone is fucking up so badly that you would like to kill them!