Author Existence Failure: The story was conceptualized by Siobhan Dowd before she died. So Patrick Ness ended up being the writer of this book.
Acclaimed Flop: Despite an 87% rating on Rotten Tomatoes, the film only just about broke even at the Box Office in foreign countries and not even in its co-produced countries: United Kingdom and United States. However, in its native Spain, it was the most successful Spanish film in 2016 and where it grossed most of its money in the box office (over $28 million) though it did not surpassed Bayona's previous smash hit The Impossible.
The Other Marty: The film's teaser trailer for the Spanish dub had Salvador Vidal, who is the main voice actor for Liam Neeson since Schindler's List, as the voice of the Monster. The next teaser had Miguel Ángel Jenner and the third trailer had Camilo García (main voice actor for Anthony Hopkins and Harrison Ford among many others) who went for the final role and previously voiced a then unknown Neeson in The Bounty. While it's unknown the reasons of the creators' decision, it was probably done to give the Monster a rough voice like Garcí instead of Vidal's soft baritone voice.
Production Posse: Óscar Faura (cinematography), Belén Atienza (producer), Fernando Velázquez (music composer) and Bernat Vilaplana (film editor) who worked with Bayona since The Orphanage. Geraldine Chaplin has a very small role as Conor's headmaster and Tom Holland made some small stand-in appearances for the Monster in a few scenes. Most of them went to work again with Bayona in his next film: Jurassic World: Fallen Kingdom.