Originally Posted by dogu

For those unfamiliar with the local accents, it's helpful to remember the 'law of conservation of Rs'.
Rs are neither created nor destroyed, they simply move from places they belong to places they don't.

In Boston, one 'pahks the cah on Havahd yahd' (Translation for those south of the Mason-Dixon line 'Parks the car on Harvard yard).

For what it's worth, the missing Rs go to the end of words like law (lawr).

Now think how a Bostonian would pronounce 'Car Keys'...and the joke is revealed.