Zarek's foot impeded the boy-man's breath, but he didn't let up—not until he heard the full story.
When he finally managed to squeeze out the rest of the information he needed from the sniveling coward, he paused, falling into his thoughts.
He had learned more in the last few minutes than he had from an entire day of following after this boy-man.
This "key" wasn't really a key, but instead access to a certain region. It didn't open a door, but would instead allow one to pass through a barrier that would otherwise block you.
According to the boy-man, it could be used to slip through the Matrices blocking the powerful beasts and Turned from this world and keeping them in a deep sleep.
As Zarek had expected, proximity was one of the factors that would unleash those monsters, but time was another.