Is this cosmetic surgery or something else? Either way, Elias is now wary and even rather scared of his mother. Some previous trauma has let to a strange situation; she refuses outright to speak to Lukas. Elias urges his brother in private to apologise - but for what?
Every minute that goes by ratchets up the mystery and the unease. The boys are evidently permitted to keep a tank of hissing cockroaches in their room. One twin has a crossbow. Suffice it to say that in both these cases, Chekhov’s rule about the gun witnessed in Act One applies.
We witness the awful result of a paranoid thought entering the sons’ heads. She is not the nice loving mummy they knew, the mummy who once loved to sing them a lullaby - and doctors have removed a birthmark which they consider the definitive proof of her identity. As near-identical twins they attach supreme importance to tiny details like this. Their conclusion is that this woman is an impostor and she must be tortured until she reveals what she has done with their real mother.
There are some gruesomely unsettling scenes and moments, particularly at the beginning, although Franz and Fiala have an exasperating habit of leaving scenes unfinished, moving enigmatically on to the next scene. Perhaps a more unassuming genre director would have tightened this movie’s cables a little, so that it had more tension and less revulsion. At all events, it delivers some nasty shocks.