To misquote the book that Netflix's The Haunting of Hill House. Whereas the first series was loosely based on Shirley Jackson's book of the same name, The Haunting of Bly Manor is based on Henry James' famous ghost story The Turn of the Screw.
One of the most chilling features of The Haunting of Hill House were the dozens of ghosts carefully hidden, out of focus, in the background of shots throughout the series. These ghosts were never acknowledged by the characters, and in fact it's possible to watch the entire show without ever spotting them. Once you know to look for them, however, you'll start seeing them everywhere.
The Haunting of Bly Manor stars Victoria Pedretti (who played Nell Crain in Hill House) as Dani Clayton, a young American woman who is hired as an au pair for two orphaned children, who are living in their family's sprawling estate in England. Hoping to escape from ghosts in her own past, Dani finds more waiting for her at Bly, and starts to fear that two spirits in particular are preying on young Flora and Miles. One such ghost is Peter Quint, played by Oliver Jackson-Cohen (another actor from Hill House, having played Luke Crain in that show). If you look closely at the shot of Flora and Miles running towards the manor you'll see Peter lurking on the parapet, recognizable by the same clothes he wears later on in the trailer. And he's not alone.
Camouflaged against a hedge to the left of the car is a figure dressed in brown robes and a hat. It could easily be mistaken for a statue, but Bly Manor's drive is very symmetrical in design and there's no figure in front of the corresponding hedge on the other side of the entrance. The two hedges are also shown later in the trailer, with nothing in front of them. Clearly Bly's spooky residents aren't afraid of the daylight.
The trailer also showed other ghosts, like an eerie figure on the floor behind Flora while she's hiding in the attic, and a chilling tease of a woman with no eyes ri from the surface of the pond. It looks like Bly Manor is just as infested with restless spirits as Hill House was - and it could prove to be just as deadly.