大比丘三千威儀 2.28

2.28

There are further five matters: first, if the cup placed before oneself is set crookedly, one should straighten it, and if it is not straight, one must not eat; second, if eating utensils have dropped, one should not eat from them again; third, if someone comes to add food, one should always point to follow along; fourth, when one does not see them coming, one should not eat; fifth, when the food is before oneself, one must not taste it beforehand.