Cinematographer Luis Cuadrado was going blind at the time this film was made. An assistant would take Polaroids of the scenes and Cuadrado would direct the lighting by looking through a magnifying glass at these pictures. In 1980 Cuadrado committed suicide after he went completely blind and the tumor in his brain became too painful to face.
According to Víctor Erice, Ana Torrent, who was six years old at the time of the shooting, believed the Frankenstein monster existed in reality. The first time she saw the actor playing the monster in full makeup, she was completely terrified and later she asked him why he had killed the little girl (in the Frankenstein (1931) movie). The actor didn't know what to answer.