I found a version of "Hoochie Coochie Man" that I like on Youtube. At 2:37, the guitarist plays a note on the G string fifth fret, then a G and D string chord on the seventh fret, then he's back to G string fifth fret, then a hammer-on to the G string sixth fret.

The notes and chords have a crunchier sound to them than others in the song. I can't figure out what he's doing (unless he has a pedal for just those four notes/chords, which I somehow doubt). I've tried various degrees of muting, which is all I can think of.

Any ideas or suggestions? The video is here: http://www.youtube.com/watch?v=zy5i4tQYUzA&feature=related

Thanks for any replies.
First he's muting, and then it's just heavier attack with his pick on that section. No effects or anything like that.
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