Due to the extremely low budget available to create the movie, only the two main characters wear real contact lenses. That's way almost any other zombie has "regular" eyes. Any other zombie eyes, including the zombie scene of Enrique Selfa, was digitally added in post production.
During the production, the local police department of Linares city was aware of the movie, but apparently the secret police was not. One day the main character, Jose Casas, was alone in the street with a prop gun while all the crew was inside a building recording him through a window. He almost got arrested, when the crew noticed what was happening and explained everything to the police.