Speaking of his mother in chapter 2, Grendel tells us, "She'd forgotten all language long ago, or maybe had never known any" (28).
Considering her son's considerable eloquence, the mother's lack of language poses some tough questions - not the least of which is: how and when did Grendel learn to speak?
Yet, near the end of the book, mother does manage to utter some significant sounds. "'Dool-dool,' she moans. She drools and weeps. 'Warovvish,' she whimpers and tears at herself" (145-146). What could this mean?
"Warovvish" is fairly resolved on 149 as "Beware the fish," which could easily be understood as Beowulf. One correspondent on The Grendel Board makes the connection to "Beowulf, who was beardless, and whose prowess in the water was widely noted."
The same correspondent notes, "Every event, person, and even the entire story, has an essential duality of meaning (dool-dool, better spelled dual, dual): 1. How it relates to Grendel and the purpose of telling the story; and, 2. How it relates to the reader, which is in essence Gardner's message."
Given this possibility, it may be that Grendel's mother reaches deep down into her most ancient memory in order to warn her child of impending danger...and at the same time provides the reader with a key to recognize the duality of both the novel and (possibly) of Existence itself.
And teacher Liz Bucarelli writes:
According to one online source, the Scandinavian word "dool" means "delay" or "sleep."
See a brief discussion of the philosophical problem of dualism at the Internet Encyclopedia of Philosophy.
A most curious scholar might also seek out: