Um. I don't think I'm explaining this well at all =(. I remember being in Hong Kong and seeing these Chinese characters and thinking it made no sense -- maybe like seeing "car freezer oops" in the middle of a normal sentence. So all the characters themselves were something that I could read and would normally make sense, just as "car," "freezer" and "oops" all usually make sense. But in the context, it made no sense at all unless you spoke Canto (ex. say "car freezer oops" was somehow Brit-speak for "lawnmower").

But of course the thing that makes it more complicated is that spoken Canto doesn't sound like spoken Mandarin at all. They share a lot of the same words and phrases (like American-speak and Brit-speak), but the pronunciation of all of these are usually so different that a Mandarin speaker won't be able to translate what a Canto speaker is saying. But then there are the times when the words and phrases are different, as with the "car freezer oops" bit.

Um, I'm not sure if that made sense at all...

Also, OMG Chinese puns. You have no idea! None! (says the person who had to painfully memorize all random pun allusions for poetry in Chinese class)