It seems to have been a large cup, and of great price, and much used by Joseph. In the sack's mouth of the youngest, with design to discover their intentions and affections towards Benjamin, whether they did envy him, and would desert him in his danger, as they did Joseph; or would cleave to him; that hence he might take his measures how to deal with him and them.
Related Commentaries of Genesis 44:2
Genesis 44:2
2 And put my cup, the silver cup, in the sack's mouth of the youngest, and his corn money. And he did according to the word that Joseph had spoken.