If you take a good, hard look at the Table of Contents of this novel, you will immediately begin hear and understand Percy's voice. With chapter titles like, "I Become Supreme Lord of the Bathroom," and "We Get Advice from a Poodle," Percy injects some hilarious sarcasm and a bit of irony into his storytelling; he sets us up with a big declaration ("I Become Supreme Lord…") and then turns this declaration on its head ("…of the Bathroom"), taking us readers by surprise and catching us off guard.
Percy pretty much downplays the fact that he's battling monsters and retrieving Zeus's symbol of power, demonstrating to us his humility. It's pretty clear that Percy is not a typical Greek hero in the way that he's so laid back and nonchalant at times. He even tells us in the beginning of the story, "Look, I didn't want to be a half-blood" (1.1). The life of a hero is not necessarily one that Percy is excited about, and his chapter titles and storytelling reflects this attitude. He's a hilarious, witty, and matter-of-fact storyteller, telling it like it is as he notices everything around him.
Take for example this lovely moment:
Once I got over the fact that my Latin teacher was a horse, we had a nice tour, though I was careful not to walk behind him. (6.1)
By underplaying the fact that his Latin teacher is a centaur, Percy emphasizes and demonstrates to us just how crazy the whole situation is. On top of all that, he manages to be practical too, telling us he was careful not to walk behind Chiron for fear of stepping on any horse droppings. He takes a perfectly earth-shattering discovery (his favorite teacher is a centaur) and paints it as an everyday occurrence.