Juraj Herz's original intention was to reveal at the end that the two sisters are actually one person and the film is about schizophrenia. However, this did not please the head of Barrandov Studios and Herz had to change the script.
It was not clear from the beginning that both sisters would be played by the same actress. Juraj Herz even gave Iva Janzurová the choice of which one she wanted to play. However, before the actress decided, he informed her that she would play both of them.
In Aleksandr Grin's short story, of which the film is a loose adaptation, the sisters are named Jessie and Morgiana. In the film, they were renamed Klára and Viktorie, while the titular Morgiana is the name of Viktorie's gray cat.
In 1973, the film won the Golden Hugo Award at the Chicago International Film Festival.