He understood a great many things about his parents, and he knew that many times they didn't like his understandings and many other times refused to believe them. But someday they would have to believe. (4.6)
Danny's understandings include what he reads in his parent's minds and the things Tony shows him. Are these understandings supernatural or natural?
[…] he kept telling himself, over and over, that the things Tony showed him didn't always come true. (9.34)
This is what's going on in Danny's head when he first arrives at the Overlook. Tony has already showed him that something dreadful is going to happen. Danny doesn't yet understand that the reason the visions don't always come true is because people sometime change their minds. Predictions of the future are based on the state of affairs at the time of the prediction.
"What you got, son, I call it shinin on, the Bible calls it having visions, and there's scientists call it precognition. […] They all mean seeing the future." (11.78)
Even though Halloran has been shining all his life, he doesn't really understand that much about it. For instance, he tells Danny what he already knows, that the visions don't always come true. Of course, he doesn't tell him why and might not know himself. In addition to seeing the future and reading minds, Danny's ability allows him to see the past too, in the form of the Overlook's ghosts and other phenomena.
"You shine on, boy. Harder than anyone I ever met in my life, and I'm sixty years old this January" (11.7).
The idea, spoken by Halloran here, that Danny's ability is really strong is reinforced throughout the book. Apparently, he's able to perceive the supernatural world of the Overlook more intensely because of it. In "Characters" we wonder if Jack has the shine, too, considering how many ghosts he meets at the hotel.
"I'm going to eat you up, little boy. And I think I'll start with your plump, little cock." (41.20)
Some readers find this one of the most disturbing passages in the novel. It suggests that even more so than the woman in 217, the evil at the Overlook manifests in sexually predatory behavior. Here, it seems directed at Danny because he's a child. It makes us fear all the more what the Overlook will do to Danny if something doesn't give.
Delbert Grady and Family
"The manager," Grady said. "The hotel, sir. Surely you realize who hired you, sir." (44.57)
In Jack's "Character Analysis" we look at the way King plays on the idea of The Overlook as some kind of annex of hell, which would make "the manager," the devil. What do you think? Who or what is the manager Grady is talking about?
"Let me out, Grady. I'll take care of them." (48.11)
Like the woman in 217, Grady has some control over the physical world. In this case, he lets Jack out of the pantry, after Jack agrees to kill Wendy and Danny. These touches make it difficult to avoid supernatural explanations, unless there's some evil mastermind hiding in the hotel, creating all this with special effects.
(Real psychic phenomena or group hypnosis?) (50.4)
Wendy comes to believe the former, but is the latter a possibility. If so, who or what is hypnotizing the Torrances?
The door to one of the rooms jerked open and a man with a green ghoulmask on popped out. "Great party, isn't it?" He screamed into her face, and pulled the waxed string of a party favor. (52.7)
What a bummer. If not for the cameo appearance of this ghost, Wendy might have gotten to the quarters before Jack breaks her vertebra with the mallet. The hotel is doing its best to help Jack kill Wendy.
What remained of the face became a strange and shifting composite. […] Danny saw the woman in 217; the dogman; the hungry boy thing that had been in the concrete ring. (55.76-78)
This is after Jack destroys his face with the mallet. The passage reinforces the idea that he's possessed by the Overlook and no longer acting of his own free will. Do you buy it?