Rowling continues in chapter 2 to develop the theme of Harry’s innate nonconformity to muggle society against the Dursley’s desire to suppress his individuality.
Another element is added here in that Duddley is Harry’s opposite. His parents spoil him, but he doesn’t seem to be much of an individual himself. He’s more like a fat lump that doesn’t do much of anything. So he gets rewarded for his muggle conformity while Harry gets punished for his latent individuality. Rowling gives Harry’s individuality a physical symbol in his lightening shaped scar.
Petunia Dursley tries to hide his scar by giving him an awkward haircut so that his bangs fall over it, just as the Dursley’s try to hide Harry in a cupboard. His hair, uncoincidently, magically grows back. As hard as they try, the Dursley’s can’t suppress Harry’s innate individuality.
The Dursley’s, of course, warn Harry about the trip to the zoo for Duddley’s birthday, “any funny business–anything at all–and you’ll be in the cupboard from now until Christmas” (24).
Harry, as we’ll probably all know by know, can talk to snakes (which will be more important later but for now just consider it another way Harry doesn’t conform to muggle society). He magically makes the glass disappear, symbolically expressing his individuality while setting the snake loose.
Harry gets punished by being exiled to his cupboard, where he ruminates about his unknown origins, why he doesn’t conform, and wishes he might find someone to help him escape his surroundings.