וְהֵם֙ לֹ֣א יָֽדְע֔וּ כִּ֥י שֹׁמֵ֖עַ יוֹסֵ֑ף כִּ֥י הַמֵּלִ֖יץ בֵּינֹתָֽם׃
And they knew not that Joseph understood them; for the interpreter was between them.
Read kabbalistic (mystical) interpretation of Genesis 42:23: and classical mystical sources.