What's with the black smudges on him in the last panel? Is he so inept at using a pencil that he gets markings on him everywhere? Did he get mugged and beaten up and thrown into a trash can? ...oh, that's a DIFFERENT character. ...still, why all the black smudges?
I thought I snagged the joke, then I saw it was someone else writing the letter and the joke escaped my grasp again. What am I missing? And don't say the pig's the editor of the comic, because while likely, that doesn't fall in cleanly with the rest of the letter that the rat began with.