Symbolism, Imagery, Allegory
Question: When is a cat not simply a cat? When he's Angus, wreaking havoc on Georgia's life—just like the process of growing up does.
If you've done any coming-of-age ever then you know it's a doozy of a process. Everything is so chaotic and confusing, especially when hormones are in the mix, which they most definitely are for Georgia (those boobs didn't grow themselves, you know). As he prowls around her house, Angus is a purring and hissing reminder that Georgia's a girl in the throws of growing up, which leaves her alternately hissing and purring herself depending on her mood.
Angus, however, isn't simply a nuisance. Sure, he is unaffectionate and destructive, but when he goes missing, Georgia's world threatens to unravel—or at least her romantic world, since things aren't looking so good on the Robbie front. In other words, the chaos of growing up that Angus represents is a good thing, even if it's a hard thing; there's no growing up without it.
Importantly, though, while Angus's return marks Robbie and Georgia finally getting together—a real mark of maturity in Georgia's eyes, particularly since Robbie previously dismissed her on the grounds that she was too young for him to date—Georgia discovers she's moving to New Zealand almost immediately afterward. The thing she thinks is key to growing up, then (romance with Robbie), actually probably isn't. After all, Angus will be joining her (we presume), but Robbie will be staying behind. To explore this further, read up on feminine accessories elsewhere in this section.