Watch the Cool Licks: 1 online guitar lesson by Muriel Anderson from 1-2-3 Fingerstyle Guitar

This is a chromatic sounding cross-string technique. Even though some of the notes aren't in the scale, they go by quickly enough that it doesn't matter to the ear, and just the consistent shape on the guitar provides structure.

You can check out some music by Buster B Jones or Phil Keaggy for other cool cross string riffs.