This is the main "groove" part of the song. Now, let's pay very close attention to what's going on rhythmically here. When you watch the Full Video, listen carefully to what the guitar and drums are playing in this part. Basically, both instruments are playing in two different time signatures at the same time, which means we have a polyrhythm (or polymeter). The guitar is repeating a 7/8 riff, while the drums are keeping a consistent 4/4 groove underneath. Applying this kind of rhythmic concept to your songwriting can produce some very cool and creative musical ideas.
As far as this exercise goes, be mindful of the palm mutes you'll be playing on the 3rd fret of the Low E string. You may also have to bar the 3rd fret with your index finger in order to play the occasional note on the 3rd fret of the D string.
When you're ready, let's turn the page to Exercise 4!