[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-|

Then for the middle part (300 people...) play the main riff twice.
Then play the verse through once more.
Then for the second chorus (exactly the same words as the first) just play the
main riff four times.

[Outro]
E|-----------------|
B|-----------------|
G|-7---------------|
D|-7---------------|
A|-5---------------|
E|-5---------------|