I worked this out whilst listening through PUNGENT EFFULGENT, its quit simple all you have to do is
get the timing right.

Riff 1

G--------------------
D-----------------1--
A-2-2-1-2-----1-2---3
E---------2-3--------

Riff 2

G-----------1-3-4-3-1--------
D-------1-3-----------3-1----
A-2-2-3-------------------3-2
E----------------------------

Order

Play Riff 1 a number of times quietly before it kicks in then play them in this order.

Riff 1 = 3 times
Riff 2 = 1 time