Mar adentro
During casting discussions between Bayona and del Toro, Bayona expressed a desire to see Belén Rueda in the lead. Bayona admired her after seeing her performance as Julia in Alejandro Amenabar's "The Sea Inside". Del Toro appreciated this choice, as he admired her as an actress and liked that Bayona was casting her against type. Bayona asked Rueda to watch "The Innocents" and "Close Encounters of the Third Kind" to prepare for the role. Another actress Bayona desired for the film was Geraldine Chaplin in the role of Aurora, the medium. Bayona stated that he wanted the film to have "the mood of 70s Spanish cinema and Geraldine starred in one of the best movies of that decade, Carlos Saura's "The Secret of Anna", as the ghost of the mother. It made sense to have her play the medium." Bayona was nervous about filming with Chaplin. To break that tension, on the first day of shooting with her Bayona hid under a bed during a scene which required Chaplin to portray Aurora kneeling down near it in the dark, and he grabbed Chaplin's leg when she did so. Aurora's scream in the film is Chaplin's actual frightened scream as Bayona grabbed her. Roger Príncep's test-screening was one of the first for the role of Simón. Bayona test-screened over four-hundred children during two months before making his choice to cast Princep. Edgar Vivar was cast in role of Balabán; Bayona knew him through his work on the Mexican television series "El Chavo" and sent him an invitation for the role through e-mail.