What does “mirilla” mean in Spanish?

In this animated horror story, a girl checks who’s at the door late at night by looking through the mirilla — the peephole set into her front door — and what she sees through it drives the whole story. Mirilla comes from mira (“sight/view”), itself from the verb mirar, “to look,” with the diminutive -illa shrinking it to “little viewing spot” — the everyday word for the fisheye lens on any Spanish door.

The diminutive -illa/-illo is a productive pattern worth noticing elsewhere: ventana (window) → ventanilla (a small window, like a ticket counter’s), puerta (door) → portilla (a small gate or hatch). In the story, the girl looks through the mirilla twice before deciding whether to open the door — the peephole is both her only source of information and the thing that finally warns her not to trust what she’s seeing.