Relating these to Australian slang words, if "banger" relates to a sausage, then "cocky" would be short for a cockatoo. A cockatoo is a bird that is a native to Australia. Though "cocky" may also mean someone who is overconfident in a bossy way, seeing as how banger is used as a slang word, cocky as a cockatoo is more fitting.
I love this book!
But I am not sure what you mean with your question (it's missing a verb).
But if you're looking for more information: The sense of guilt in this book is often created by other characters, when they're trying to come to terms with some tragedy (such as many characters being blamed for Sophie Mol's death). So in a way, guilt can function as an explanation. But also it's created by the social norms (as when Estha feels guilty because of the Orangedrink man).
