ONE should not use a slice of bread to cover therewith a dish. One should not wipe the dish with a piece of bread and lay it on the table, for he disturbs the mind of his neighbor. For the same reason, one shall not bite off a piece of bread and place the remainder in the dish intended for another person. One should also not drink from a goblet and give the balance to another one to drink, for it may cause danger to life. It happened that R. Aqiba stopped at the inn of a certain person, who offered him a goblet, first tasting its contents, and R. Aqiba told him to drink the whole of it. He offered him another one, first having tasted it. R. Aqiba told him to drink it all, until Ben Azai said to him: "How long wilt thou continue doing so?" It again happened that R. Aqiba was lodging with a certain person, and he placed a piece of bread underneath the dish to support it, and R. Aqiba took hold of it and swallowed it. Said the man to R. Aqiba: "Rabbi, had you no other bread to eat than that piece with which I supported the dish?" And he answered: "First, I thought that you could burn yourself with lukewarm water (i.e., you will understand a slight hint). Now I see that you cannot burn yourself even with boiling water." One shall also not empty his cup and then place it on the table, but he shall keep it in his hand until taken away by the waiter.
Five things said Rabbi in regard to bread, namely: Raw meat must not be placed on bread, nor shall a cup or dish be placed on bread, nor shall bread be used to support a dish, nor shall it be thrown from place to place; nor shall one sit at the table when others are eating, for he disturbs their appetite. One who comes to the table to take his meal shall not take his portion and give it to the waiter, for the reason that some unforeseen thing may happen during the meal (and his portion may be needed); but he shall place it in front of him until the end of the meal, and then give it to him. Guests must not give anything to the son of the host, nor to his servant or messenger, without the permission of the host. It happened once with a man who invited three guests in years of famine, that he served them three eggs. The son of the host then came and stood in front of them, and the first guest took his portion and gave it to him, and so did the second and third. When the host returned, and found his son holding one in his mouth and one in each hand, he raised him full height and struck him to the ground, and he died. The mother, hearing of what happened when standing on the roof, was so shocked that she fell down dead. When the father heard this, he also threw himself from the roof, and died. Then R. Elazar said: "Three human beings were killed on account of this."
Sources: Sacred Texts