[Main riff]
E|-----------------|------------------|
B|-----------------|------------------|
G|-7-----10----10--|-5-----12----12---|
D|-7-----10----10--|-5-----12----12---|
A|-5---5-8-----8---|-3---3-10----10---|
E|---5-------8---8-|---3-------10--10-|

For the intro play the main riff four times.
For the verse (which is all the 'but now's) play the main riff 3 times, then play;

E|-----------------|-----------------|
B|-----------------|-----------------|
G|-7-----10----10--|-9-------9---9---|
D|-7-----10----10--|-9-------9---9---|
A|-5---5-8-----8---|-7-------7---7---|
E|---5-------8---8-|-7-------7---7---|

For the first chorus (You thought you heard a sound...) play the main riff 3
times and then;

E|-----------------|-----------------|
B|-----------------|-----------------|
G|-7-----10----10--|-9----77-9----77-|
D|-7-----10----10--|-9----77-9----77-|
A|-5---5-8-----8---|-7----55-7----55-|
E|---5-------8---8-|-7----55-7----55-|