Burrow Grubs is the 48th chapter of Inheritance. It takes the point of view of Nasuada.
Summery
This chapter is the first time we hear of the Burrow Grubs. We later find out they are from the island of Vroengard in effect of the nucular radiation. Galbatorix controls the Burrow Grubs and makes them burrow into Nasuada's elbow in a form of torture to make her swear fetality to him.