Hamlet is direct and honest with Rosencrantz and Guildenstern in Act 4 Scene 2. After the death of Polonius they question the Prince about the body, claiming they want to ensure a proper burial. Hamlet gives them nothing, knowing that Claudius has sent them. He calls them a sponge:
‘Ay, sir, that soaks up the King’s countenance, his rewards, his authorities. But such officers do the King best service in the end: he keeps them, like an ape an apple in the corner of his jaw; first mouthed, to be last swallowed: when he needs what you have gleaned, it is but squeezing you, and, sponge, you shall be dry again.’
Rosencrantz claims to not understand what Hamlet is saying and Hamlet replies:
‘I am glad of it: a knavish speech sleeps in a foolish ear.’ He believes that Rosencrantz is too stupid to understand sarcasm.
Later in this Act, Claudius dispatches Rosencrantz and Guildenstern to England with Hamlet.