Now we've come to the very fast and heavy rhythm section. Make sure you are especially warmed and stretched before playing this part! There is a lot of strain on your picking hand here, so be sure to gradually increase your speed as you practice. Don't kill yourself trying to play it up to speed right off the bat.
Most of the notes we're dealing with here are sixteenth notes and thirty-second notes. There are quite a few bursts of 32nd notes throughout the riff. When you play those 32nd notes, put extra energy into relaxing your picking hand. Consciously focus on your picking hand being relaxed. That actually applies to anything you play on the guitar, but it's especially important when playing strenuous riffs like this.
In the second half of bar 16, we come to the end of the riff. Be sure to watch how I play this part in the video. I'd recommend starting out on the 3rd fret with your index finger, then sliding your index up to the 7th fret, then back down to the 5th. If you use your index finger for those 3 notes, it will set you up perfectly to continue the riff by hammering on the 7th fret with your ring finger, etc.
On to Exercise 4!