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.

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

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

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

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

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

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

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

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

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

There's also a face visible below the ladder.

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

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

Then there's someone behind Liv once again.

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

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

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

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

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

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

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.

And this isn't a ghost exactly, but this statue's head moves when Liv enters this room...

Here it is as she exits, watching her:

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

And again when he inspects the mould in the basement.

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

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.

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

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

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

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