It is interpretive, a narrative, a report and its thesis cannot be debated.
The conflict in this excerpt creates suspense by making the reader wonder
When Grendel says Unferth's "beard and hair hung straight down like seaweed", the literary device used is SIMILE.
Simile is comparing two unrelated and dissimilar things, people, beings, places, and concepts using the words "like", "as" or "such as"
Beard and Hair was compared to seaweed using "like".