Every time Jack sees a putative “ghost” Stanley Kubrick has him looking at himself in a mirror. Even when he speaks to Grady in the bathroom if you look closely Jack isn’t looking directly at him. He’s facing Grady but his eyes are looking into the mirror. Even when Lloyd and the old woman in room 237 are present Jack is looking into a mirror. There's only one implication you can draw from this; Jack is talking to himself as he looks at his own reflection in these scenes. From the audiences’ perspective this cannot be seen. But it is what Jack is seeing. Stanley Kubrick has him looking at the reflection of himself in a mirror.
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