According with Álex de la Iglesia, Raphael watched the movie before the public premieres, and he didn't like voice acting of the actor who played him. De la Iglesia offered him to dub himself, and finally is Raphael's voice which is heard in the movie.
Álex de la Iglesia's first film not co-written by Jorge Guerricaechevarría. The director wanted to tell the story badly but his writing partner didn't really connect with the material, so De la Iglesia wrote it on his own.
The famous "Wilhelm Scream" can be heard several times in this movie, but most prominently when two midgets are thrown out of the Wonderland Cirgo tent at 20:15.
A still of Cannibal Holocaust (1980) appears in opening credits. Luis Varela, who plays Manuel the veterinary in this film, dubbed Carl Gabriel Yorke in the Spanish version of Cannibal Holocaust.
Edward James Olmos was interested in working with Álex de la Iglesia. He was in talks to play one of the main characters, but finally he couldn't accept because of his busy schedule.