Julio Medem wrote the part of Alba for Elena Anaya. When the actress accepted the role, she and Medem went to Russia to cast the perfect Dasha. After seeing a lot of actresses and models, they found the perfect one, but the night before this woman was to fly to Spain to start rehearsals, her husband read the screenplay and forbade her to play the role which involved nudity and lesbian lovemaking scenes. However, after returning from Russia dejected, Medem and Anaya found Ukrainian-born model Natasha Yarovenko while casting in Spain, specifically in Barcelona, who accepted the role.
When Alba tells Dasha that her two-wheeled vehicle is called the "Aspasia," Dasha smiles and says she knows after whom it was named. Aspasia was the lover (and maybe wife) of Pericles, the leader during Athen's Golden Age in the Fifth Century B.C. when the arts flourished and the Parthenon was built.
The voice of Sasha, Natasha's (real name Dasha) twin sister is actually voiced by the same actress Natasha Yarovenko which was recorded during post production.
The song sung by Natasha/Dasha and Alba in the shower is "Nel Blu Dipinto Di Blu," commonly known as "Volare" in the U.S. It was a worldwide hit (including number one in the U.S.) for Domenico Modugno in 1958. The lyrics describe a dream that the singer knows will never happen again in which he is painted blue and flying ("volare") and singing ("cantare") in the sky. A non-literal English translation of the song was a hit by Bobby Rydell in the U.S. in 1960.
Based on the premise of Matias Bize's chilean film "En La Cama"