Just a few comments on how to play the song... First of all: The most important thing is to get these open strings to sound as 
clear as possible! You don't want to graze or touch these open strings at all or it will mess up the sound. The exception to th
at rule is Riff 3 - see below.

Riff 1: Some tabs add a bend here - and yeah, you can give the G- and C-string a little bend 
without hitting them again. But it's not much I think. This riff gets its ominous sound from hitting the open F-string twice an
d letting it ring. You can also give the string a sort of extra strong hit to emphasize it. And make sure to let that D-powerch
ord ring!

Riff 2: The second note in this one's a bit strange as you can see on live videos that he's not changing the chord
 or does something extra-special with his picking hand. Or at least it seems that way... So I guess he's just picking the A-not
e on the G-string. You can give it a little bend but on live-videos it doesn't seem to be that much of a bend. And once again: 
Make sure to let that D-powerchord ring!

Riff 3: Once again there are tabs that add a bend to that riff. But to me it seems 
pretty clear that he's just playing these open strings. Important thing: Right after hitting the open strings use your fingers 
to mute them or you will get a pretty messy sound.

Riff 4 + Riff 6: Yeah, it's pretty obvious - but for the sake of complete
ness: You have to let the notes ring - especially the open strings.