Miss Manners: Speaking with your mouth full isn't helped by putting your hand up to your face

DEAR MISS MANNERS: I have noticed, even among people I otherwise consider well-mannered, a new trend. During a meal, when someone wants to speak while eating, they hold their hand up to obscure their mouth. They seem to know that speaking with their mouth full is rude, but they also seem to think this action fools me into thinking their mouth is not full, despite their having just put a forkful of food into it. I was taught that if someone asks a question or makes a comment requiring a...