the bass part for this song is as groovy as it is easy.
the same basic part is played throughout the song. variations are often thrown onto the 
end of it (so fool around and find your own!) to transition back into the beginning, but 
this is the basic rhythm. to play it, simply jive like so:

G||------------------------|
D||---------------------2--|
A||----------------2-------|
E||--2----5--2--5----------|

and there you have it.