its called a pinch harmonic, its where you lightly brush your thumb agains the string after picking it. you might wanna look at some tutorials on how to do it
it's a pinch harmonic sir...but that one wasn't very good...i have a bunch up in my skills if you want to hear better ones...and i also have a lesson on youtube...www.youtube.com/user/chuckmehh teaching you how to do them. good luck!
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