HAMLET         Why, look you there! Look how it steals away –

My father in his habit as he lived.

Look where he goes even now out at the portal! (Exit Ghost.)

GERTRUDE    This is the very coinage of your brain.

This bodiless creation ecstasy

Is very cunning in.     (3.4.132-137)

Look, look! says Hamlet, why, look you there! right THERE! can’t you see it, see HIM? Look how it steals away—going, going, so silently, so subtly, stealthily. My father in his habit as he lived, wearing his old familiar dressing gown, exactly as he did, when he was alive, exactly as I remember him… This is the first time Hamlet’s explicitly identified the Ghost as his father, and Gertrude might well recoil, look shocked, disgusted even. Hamlet’s tracking the Ghost with his eyes, perhaps a pointing finger, can’t you SEE, look where he goes even now out at the portal! He’s gone. (Apparently through the door, no wafting through walls here.)

Gertrude’s appalled: this is the very coinage of your brain. You’re seeing things; it’s all in your imagination. (And this interpretation forces her to concede, of course, that Hamlet is indeed mad.) It’s a symptom, you’re not well, this bodiless creation ecstasy is very cunning in. When you’re—not yourself—you see things that aren’t there, I know it seems real, but it’s not, it’s not, it’s your mind playing tricks on you!