Final answer:
Hamlet accuses Rosencrantz of being a sponge, metaphorically highlighting his disloyalty and ease of manipulation by King Claudius.
Step-by-step explanation:
When Hamlet speaks to Rosencrantz in Act IV, scene 2 of Shakespeare's play Hamlet, he accuses Rosencrantz of being a sponge. This metaphorical insult is Hamlet's way of saying that Rosencrantz soaks up the king's favors, rewards, and protection, but in reality, is easily squeezed and manipulated by those in power to serve their purposes. The underlying implication is that Rosencrantz is not loyal to Hamlet and that he allows himself to be used by King Claudius for his own ends, just like a sponge that absorbs whatever liquid it comes into contact with and then yields it up when pressured.