During a meal it's better not to talk because if you talk, you don't chew properly. I'm talking about materially, not to mention spiritually. Also, sometimes when you talk, you swallow [your food down] the wrong channel. Instead of going to your stomach, it goes into your lungs or your nose and causes you trouble. Sometimes you can die from it! So since ancient times people have said that when you eat, you shouldn't talk.

That's the logical explanation but there's another explanation, which is that most of the time the devil goes through the mouth because it's the widest opening of all and we keep it open most of the time. If there's anything that wants to possess us, it can enter through the mouth very quickly. So when we eat and open the mouth and talk all the time, the devil will hear it and then go inside with the food. Or it will contaminate our food and make it indigestible for us or make it poisonous or make it do something troublesome when it enters our body.

Sometimes we have an infectious disease and we don't even know it yet. It may have entered but hasn't developed yet in our body so we don't know we have it. If we eat together and talk, we breathe all kinds of germs into the food, and then both people have to inhale and eat the food that's infected by our germs. 

So while eating, it's better if we don't talk. If we have to talk, it's better not to talk directly into the food. It's not like you have to crawl on top of the table and talk to each other! Because then, of course, your mouth water and breathing will cause all the germs to go in through the food as well. Maybe we don't see them but they're there.