There's a lot to take in the first time you watch The Haunting of Hill House on Netflix, so you might not have realised there are a lot of ghosts hidden in the background. Suddenly, some of the most ~normal~/not scary scenes become a whole lot spookier. Here's all the hidden ghosts I could find...
Episode 1: "Steven Sees A Ghost"
The first couple of minutes of The Haunting of Hill House feature shots of the house with Steven's voiceover. Look closer as the camera pans over the stairs – there's a ghost hidden there.

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Later, when Hugh wakes Steven, there's a ghost behind him.

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And as the two of them run down the stairs, there are two ghosts off to the side.

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Finally, when Liv talks to Mrs Dudley and Steven, there's a ghost behind her.

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Episode 2: "Open Casket"
When Shirley discusses the forever house with Liv, there's someone in the garden behind her.

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And there's someone in the background of the shots of Liv, too.

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Episode 3: "Touch"
There's a face in the door when Theo enters the kitchen.

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And there's someone lurking in this shot of Theo and Luke.

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There's also someone in the background of this shot, when Theo lowers Luke in the dumbwaiter.

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There's a ghost standing off to the side when Theo investigates the basement.

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There's also a face visible below the ladder.

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And after Theo gets a vision of Liv's death, you can see this ghost lurking in the background again.

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There's also this ghost watching Theo as she moves through the house.

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Then there's someone behind Liv once again.

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And when Hugh is leading Luke and Nellie out of the house on the last night, there's a ghost behind them.

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Episode 4: "The Twin Thing"
There's someone lurking when Luke first gets his "big boy hat".

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And as Liv and Hugh discuss the history of the house, there's a ghost in the background.

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You can also see a face in the cabinet when Luke and Nellie are in the kitchen.

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Episode 5: "The Bent-Neck Lady"
In the scene where Liv accuses Nellie of writing on the wall, there's someone below the piano.

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And there's another ghost over Nellie's shoulder.

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Episode 6: "Two Storms"
You probably spotted this, but there's a lot going on in the episode, so just in case you didn't – Nellie herself appears as a ghost when Hugh first views her body.

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(She also appears later in the episode, of course, but it's even more obvious then.)
And this isn't a ghost exactly, but this statue's head moves when Liv enters this room...

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Here it is as she exits, watching her:

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Episode 7: "Eulogy"
There's someone watching Hugh when he tries to break into the Red Room.

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And again when he inspects the mould in the basement.

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And again when the police are retrieving the body in the wall.

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Episode 8: "Witness Marks"
It's not exactly a hidden ghost, but this is when we see Steven encounter the clock repairman who we later learn is actually a ghost.

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Episode 9: "Screaming Meemies"
When Hugh is carrying Luke to bed, a ghost lurks in the background.

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And when Shirley is arguing with Luke about clothes for Abigail, there's a face reflected in the glass behind them.

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Then as Liv leaves the house, there's a ghost watching in the background.

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Episode 10: "Silence Lay Steadily"
Finally when Steven watches the scene of his mother's death, there's a ghost over his shoulder.

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