Flapping-your-lips-while-you-eat and other undesirable bodily function noises

I'm not having much success at this: teaching boys how to control the inevitable burping, farting and, believe-it-or-not, flapping your lips while eating. Not to be confused with talking with your mouth full. No, the flapping-your-lips-while-you-eat might also be known as chewing with your mouth open. And it drives my husband crazy.

I encountered a teacher on the excursion the other day who obtusely said, "We've had trouble with that (after a boy let loose), have you had trouble at home?"

My instant retort was, "Of course. I live with three sons and a husband." I do have to mention that she isn't married. Maybe she doesn't have brothers either?

They have actually done a study (probably more than one, but I only know of one) that proves that men produce more methane in their intestines than women and well, you know what the result of that is, don't you?

But how do you teach them to do it discretely? Particularly at the table. Particularly as the teaching moment usually occurs while you are dying of gas exposure at the table or in the car while the rest of the family is lying on the floor laughing. I don't know.

The other day I tried to explain to them, once again, why we teach them manners. I took a longer view of things and tried to tell them that one day we would stop providing food for them and buying them clothes and housing themselves and they would have to find a job. Maybe I took the picture too far when I described the scene of them talking to a future employer over a meal and they let off bodily noises and flapped their lips. My husband was already out of his seat, aiming to destroy some giggling boys when he realised that, behind my hands, I was struggling not to break down myself. Soon we were all crying from laughing so hard. The mental image was just too strong. I've obviously been working too hard at producing word pictures in my writing and it has spilled out into my speaking.

But I still don't know what to do. Does any mother of a respectable man with real job and even a wife, have some advice for us young-ones on how to train them?