Watch the Popcorn online guitar lesson by Bill Kirchen from 30 Hot Rod Guitar Licks You MUST Know
I was doing some chicken pickin' with bare fingers, and started making this popping noise in the middle of the licks. Eventually I had to figure out how I did it. It's a false harmonic plucked with the right index finger on the (let's say) 5th string, damped with the knuckle of the right thumb which rests on, and then plays the 4th string. Does that help? Didn't think so. Let's watch.