SARAH: If Claudius hears about what is going on, Hamlet knows he will be in great danger.

RALPH: So when Hamlet rejoins Horatio and Marcellus, he demands that they swear an oath of silence.

SARAH: But then things get a bit odd. The ghost cries out from underground, and Hamlet responds in this jovial fashion.

RALPH: "Ha ha, boy, sayest thou so? Art thou there, truepenny? — Come on, you hear this fellow in the cellarage? Consent to swear."

SARAH: Hamlet moves to a different location. But then the same thing happens; the ghost cries out and Hamlet again responds jokingly.

RALPH: "Well said, old mole. Canst work i'th' earth so fast? A worthy pioneer! — Once more remove, good friends."

SARAH: Since Hamlet has just found out that his father was murdered, his lighthearted manner seems very bizarre. Ralph, let's explain what's we think is going on.

RALPH: Well, Sarah, in Shakespeare's day, miners were a common source of supernatural stories. They thought that any strange sounds they heard in a mine shaft came from spirits living in the earth that they had disturbed.

SARAH: They believed that the best thing to do in this situation was to move to a different location, and to act nonchalantly; kind of like whistling when you're afraid. 

RALPH: And that's exactly how Hamlet behaves — but not because he necessarily believes in evil spirits moving around underground.

SARAH: That's right, Ralph. It's because Hamlet fears that the soldier Marcellus may talk; and if he does, it would be better if his story resembles a typical miner's tale. That would be less likely to attract Claudius's suspicions.