Try hitting them at different places above the pickups, the closer to the neck you get, the more deeper you get. If you want that really fat n' deep harmonics Zakk does, focus on the E and A strings and at the 3rd and 5th frets untill you get better. Try learning Doomsday Jesus by BLS, its a good song to get your PH's up to par, awsome song as well.
"During this line, the kid acted like he was pushing buttons on a calculator in the air. The kid played ******* air-calculator!"
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