From what I can find out just punch your fretboard but it seems not only pointless but stupid to me.
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have no idea about what you're talking about

where'd you hear about it, is there any song its featured in?
on bass its called dragontap, and i guess your supposed to like punch the strings or the fretboard of the bass to make the sound but i dont exactly understand how to do it still.

check some of these songs for what i mean: