Commentary for Genesis 44:5

IS NOT THIS THE ONE IN WHICH MY LORD DRINKETH? He did not mention “the goblet,” but instead he spoke with them as if it was known that they took the goblet. This was why he said, “Is not this, which you took, the one from which my master drinks?” They also answered him as if they do not know what he wants: How then should we steal out of thy lord’s house silver or gold?²²⁰Verse 8 here. And they further said, “With whomsoever of thy servants there be found stolen silver or gold, let him die.”²²¹Verse 9 here.

והוא נחש ינחש, we have to assume that Joseph pretended to get his information about the brothers’ personal data by consulting his goblet. Perhaps a magic formula was hidden within the goblet. Some commentators say that a wise man of Joseph’s caliber would consult the goblet as to who had stolen it, seeing that the Torah quotes Joseph as speaking about איש אשר כמוני, “a man of my type.” [he had, after all, proven that he could see hidden things, hence his name tzofnat paaneach, the one who reveals what is hidden. Ed.] It does not say in the text ינחש בו which would suggest that he consulted the goblet, but נחש ינחש, independent of the inherent power of the goblet to reveal things to its owner.

הלא זה אשר ישתה אדוני בו?, He spoke to them as if they all knew that the goblet in question was Joseph’s special goblet.