Why does Hamlet ask Guildenstern to play the recorder?

Hamlet is feeling "played" by his friends as they try to figure out his madness. He uses the recorder as an example of something played, asking Guildenstern to play him in the fashion that one plays a recorder. He carries this metaphor throughout the next several discussions until the "friends" from his past finally confess that they have indeed been sent for.

It is important to consider the fact that a recorder is a very simple instrument to play -- requiring no technique -- only an understanding of which holes to cover to produce the notes. Hamlet sets up the ultimate insult to the men when he literally hands Guildenstern a recorder and asks him to play it. Guildenstern says that he doesn't know how. Hamlet calmly comments that it is a simple enough instrument to play, but Guildenstern repeatedly says he doesn't know how. THEN, Hamlet gets his "punch line" in. He confronts them directly and says, "how unworthy a thing you make of me! You would play upon me; you would seem to know my stops (the holes that produce the notes); you would pluck out the heart of my mystery (make me sing/talk); you would sound me (make music)from my lowest note the top of my compass (a full scale)" He is making fun of the fact that they can't music from a simple recorder but they have the arrogance to think that they make Hamlet "sing" the truth of what is going on with him? They are fools on a fool's errand, and Hamlet uses this extended metaphor to show them that.