The Seatbelts
Mushroom Hunting (Albumn Version, Not Live)

Standard Tuning

Main Riff

G||-----2-4-2--2-4|----2-4-2--2---|| The Introduction (before the horns come in) has an ending 
D||o--4------4----|--4------4--2-o||  note on the 2nd fret of the D string changing between 
A||o2-------------|2-------------o||  once and twice.
E||---------------|---------------||

So after the main riff is played there is a sort of playing around with the root, 5th and octave notes. 
G|--------  This is the basic starting point. Before the bassist adds the octave B (G-4)and the 
D|-2h4----  fills coming down from the higher E (G-7). Just have fun with it.
A|2---2---
E|--------

There you go. Have fun with it.