The structure of the song is as follows: Riff A x 2 Riff B x 4 Riff A x 2 Riff B x 8 Riff A x 1 Riff D x 1 Riff B x 4 Riff C x 4 Riff C x 8 Riff D x 1 Riff C x 2 Riff D x 1 Riff C x 8 Riff E x 1 If you listen carefully you can hear clearly when the variations in guitars and riffs are used in the bit at the end. Basically riff D is used when Frank sings/shouts "caskets filled with every slaughter...." and it goes back to riff C on the line "don't freak out...". (guitaretab.com)
