Why does the Ghost disappear on the crowing of the cock (Act 1, Scene 1)?
For two interrelated reasons: first of all, as we learn from the Ghost himself in his exchange with Hamlet in Act I, Scene 5, he is doom’d for a certain term to walk the night and for the day confin’d to fast in fires – in other words, at the break of day (which is announced by the crowing of the cock), it’s time for him to return to Purgatory and to sulph’rous and tormenting flames [to] render up [him]self. Secondly, and on a more symbolic level, the Ghost in his nightly, “undead” existence is an omen of all things unnatural and unholy, whereas the cockerel – the harbinger of daylight – is, as Horatio and Marcellus tell us in Act I, Scene 1, not only a messenger of rebirth and hope in general but also of the birth of Christ: hope and holiness personified. Thus it is, too, that during the Christmas season the cock is believed to crow all night long, while evil things must hie to [their] confine: no spirit dare stir abroad, the nights are wholesome, then no planets strike, no fairy take
