The movie prominently features the Spanish rock band Héroes del Silencio: every non-instrumental song on the movie's soundtrack is by the band, Veronica listens to the band on her Walkman, Veronica's room features at least 2 posters and 1 calendar by the band, Veronica wears a t-shirt by the band through most of the night scenes.
During the eclipse viewing on the school roof, Lucia (Bruna González) views the sun through a photographic negative. The sunlight projects the image onto her face. It is the same photo--of the children's father--that Veronica brings to the séance taking place at the same time in the school's basement.
Based on true events.