Genesis 42:9

‘And Joseph remembered the dreams which he had dreamed about them and said to them, “You are spies. You have come to see the nakedness of the land.”

He had lessons which he wished to teach them. He remembered the dreams of them bowing down to him and was determined they would do it in full measure, for as they spoke with him through the interpreters they would constantly abase themselves to him. He accuses them of being spies come to spy out conditions in the land so as to report back to prospective invaders. The words must have brought a chill to their hearts. The Egyptians could be very severe on their enemies and this man clearly had the power of life and death.