] Why can't Gertrude see the ghost???

Especially since Horatio, Bernardo and Marcellus can see it too. hmmm.....

It is always a fun debate as to whether or not Hamlet was feigning his madness - was it always an act, or did he slip over into it at some point and when was that? Could this instance be "the very coinage of his brain"? He says to it "Do you not come your tardy son to chide". Could Hamlet be feeling some guilt over his hesitation and produces his father to scold him into action?