Watch the Add Simple Chicken Scratches online guitar lesson by Vicki Genfan from Acoustic Rhythm Guitar Cookbook
The chords are pretty simple. Explore the neck a bit and find a place to hold your left hand during the scratching that sounds "neutral". You will notice that at certain places on the neck you'll get different sounds, overtones, harmonics, etc. Cover all 6 strings while keeping your hand relaxed. Make sure no actual notes are coming through!