Explain Shakespeare's pun on the word "arms" in Act 5 of Hamlet?
The gravediggers in act 5, scene 1 of Hamlet have a suitably macabre sense of humor. It doubtless helps them get through a working day more effectively. Ophelia has recently passed away, and though we don't know for certain, the general consensus is that she committed suicide. As such, she would not be allowed by the Church to be buried in consecrated ground, even though she was a member of the upper class. This leads the gravediggers to indulge in a spot of witty wordplay. The gravedigger mentions that Adam—of Adam and Eve—was the first gravedigger, to which the other wonders whether he was also a gentleman, or in other words if he had a coat of arms, as any self-respecting gentleman would be expected to have. The gravedigger replies:
He was the first that ever bore arms.
He means this in the literal sense, as in those parts of the body we use to lift things. But the other still means arms as in "coat of arms," so he says that Adam didn't have any arms (i.e., a coat of arms). After all, if Adam was the first man then the concept of a gentleman didn't really exist, so he couldn't have had a coat of arms. Yet the gravedigger is still referring to arms in the literal sense and so asks the other how it was possible for Adam to dig, as the Bible says, without any arms.
Even though the setting of this scene is a graveyard, Shakespeare interjects some humor in the scene in order to relieve the tension of the previous act where Claudius and Laertes plot Hamlet's death and the coming end of the play where there will be inevitable deaths of at least some if not all of the main characters. There is a kind of "dark humor" in the fact that funniest person in the play is the man who digs graves for a living.
The pun you are referencing is in a conversation between the two gravediggers. A pun is a play onwords when two different meanings of a word are used together. The first speaker says that gravediggers hold up (continue) Adam's profession. He is referring to Adam (and Eve) the first humans. The second clown asks, "Was he a gentleman?" The pun starts when the first clown replies "The first that ever bore arms." He means had arms with which to work, but the second clown retorts, "Why he had none." He is using the second definition of arms -- meaning weapons. Clearly, Adam didn't have any weapons. The puns is extended when the first clown comes back to "his" definition and asks, "Are you a heathen? The scripture says Adam digged. Could he dig without arms?" This short scene is a clever and silly respite from an otherwise heavy and depressing situation.