大比丘三千威儀 2.28

2.28

復有五事：一者前杯著設橫當正之，不正者不得食；二者食具已墮不應復食；三者若人來有所益，常當以指隨柱之；四者不見來時不應食；五者飯食在前不得甞味。

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.