I have heard several times (including here) of a halacha (I believe I heard it is mentioned in a gemara) that discusses not taking a bite out of a sandwich when eating with others, as it may make them feel sick and end up choking. Instead, one should tear off a piece of the sandwich and put the whole piece in one's mouth.
Where is this gemara? I seek it because I would like to know if this is halacha, and learn more about this topic, thank you.