How we cite our quotes: (Page) Vintage Books, 1989
Quote #1
All the bands did the same thing. In time I began to be more amused than revolted by what they threatened. It didn't matter to me what they did to each other. It was slightly ominous because of its strangeness—no wolf was so vicious to other wolves—but I half believed they weren't serious. (32)
You know your behavior is mighty suspect if you can revolt a human-eating monster. Grendel makes a smart observation really early on in this novel: humans are scary. And they're scary precisely because they have the ability to think and plan, and yet they use that ability to maim, kill, and waste resources. Now that, as Grendel notes, is an exclusively human evil: no brute animal does these things for mere pleasure.
Quote #2
Some evil inside myself pushed out into the trees. I knew what I knew, the mindless, mechanical bruteness of things, and when the harper's lure drew my mind away to hopeful dreams, the dark of what was and always was reached out and snatched at my feet. (54)
Grendel has a complex relationship with his evil impulses. Though he can clearly lift his mind to more hopeful and beautiful things, he's constantly reminded of how he can never fully possess or participate in them. And that makes him bitter. Grendel may feel relief or even pleasure, as humans do, from the harper's song, but it's always temporary. He's been to the dragon, and he knows how it all ends.
Quote #3
An evil idea came over me—so evil it made me shiver as I smiled—and I sidled across to the table. (83-84)
There are several moments in the novel when Grendel actually has some verifiably wicked thoughts: how he'd like to knock the Shaper's head in for singing his beautiful songs, or split Wealtheow in two so that he can stop fantasizing about her. But interestingly, he almost always changes his mind and stalks away.
Sure, he eats his fair share of old ladies and disobedient children, but Gardner chooses to keep those deeds on the margin. In this case, however, we get to see an evil plan that actually comes to life—and it's scary in its simplicity. Grendel means to taunt Unferth, the cursed thane who's looking to revamp his reputation after killing his own brothers. Grendel wants to humiliate Unferth so that he, too, will slide into despair and feel the same bitterness that he feels as an outcast.
Okay, so it's pretty funny when he pelts Unferth with a pile of apples. But that is bullying, straight up. And Unferth never really recovers, even by the end of the story.