im trying to learn the solo for wet sand but i have no clue how to create that rough sound around the 4:48 mark of the song (when john's bending 21b23 and then does something that sounds really rough...???)...

ive tried a few things with my fingers but no luck.....can anyone help?? maybe if i can get a proper name for that technique i can look it up...dont really have to explain how to do it.