Everyone knows that hotels preferably isolated, ideally with very few guests make the best options for horror films.
All that sad anonymity, all that provisional space ready to be filled with something really nasty.
InCuckoo, Alpenplatz, run by the excessively friendly Mr. Konig (Dan Stevens) totally fits the bill.

Hunter Schafer in ‘Cuckoo’Neon/Felix Dickinson, Studio AAA
In horror, that has to be a bad sign.
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Where are Gretchens parents when it matters?
Once again, director-writer Tilman Singer has chosen from a reliably dog-eared horror-movie menu.

Gretchens American mom has just died.
Dad (Marton Csokas), long since remarried to a younger woman called Beth (Jessica Henwick).
Inevitably, they just dont get whats happening here.
But what is happening, exactly?
Stevens Konig calls himself a preservationist.
What he is preserving is never really specified, although we do know that spoiler alert!
I guess mad scientists gonna do mad science: Thats reason enough.
Why everyone keeps vomiting, what the protoplasmic stuff emitted by the bird-people is these things are not explained.
Perhaps theyre just there for their yuckiness.
Sorry, no idea.
Not that this really matters.
There is always a fresh lump of protoplasm or unexpected spurt of blood coming from somewhere.
He finds a fine contrasting foil in Schafer, who plays her sulky teen-turned-avenging angel absolutely straight.
It works because, however absurd her situation, we see from her face that its desperate.
None of this is quite coherent.
It might just be nonsense.
Well, it is.