For riff 1, for most of the first two repetitions each chord is
strummed once, for the last two reps they're strummed in a simple rhythm which
is easy to hear.
riff 2
|---------------------------------------------------|-----------|
|---------------------------------------------------|-----------|
|---------------------------------------------------|-----------|
|---7--7--7--7---7--7--7--7---7--7--7--7---7--7--7--|--7--5--2--|
|---7--7--7--7---7--7--7--7---7--7--7--7---7--7--7--|--7--5--2--|
|---5--5--5--5---5--5--5--5---5--5--5--5---5--5--5--|--5--3--0--|
Heavy palm-muting on the first three chords of each set of 4.