"Perspective shift," one might almost call it an "apposition of perspective" is one of the Beowulf poet's main tools for building suspense. Working within an established genre trope (of the "monster goes to hall expecting dinner, monster meets hero instead and over-commits himself, monster and hero engage in wrestling match in which monster drags hero towards door, trying to get away" variety; see Grettis saga), the poet knows his audience knows (and indeed he has liberally foreshadowed) how the fight will end. Instead of creating suspense (and horror, and delight) by keeping them in ignorance about the outcome, he does it by forcing their perspective to shift through the various characters.
The Danes (766-787a)
The Geats (793b-802)
As we see, Grendel's perspective interweaves and bookends, and is in fact at the center, of the fight. We get Grendel's perspective on his approach to the hall, and then the switch to Beowulf's perspective when Handsco is eaten. It's back and forth, blow by blow like this all the way through the first half of the scene, and then we're taken out of the hall entirely for a fairly lengthy digression on what the Danes are hearing and thinking.
Everyone in this scene is a source of dramatic irony (where the audience knows something the characters do not) except for Beowulf himself:
- Grendel does not know that he is going to die, etc.
- The Danes do not know how the fight is going, and furthermore they are confident that nothing except fire can destroy their hall (whereas the audience knows that this is precisely how Heorot is going to be destroyed, as the poem frequently foreshadows).
- The Geats do not know that Grendel is iron-proof.