There was a spider inside the peephole and they did not notice
Imagine it is the middle of the day and you are chilling at home. Suddenly, you hear a knock on the door, but when you go see who it is, nobody is there. Confused, you step back from the peephole, and suddenly, you see it.
A giant spider is sitting on the lip of the peephole, a place that was very close to your face only seconds ago. What would you do if this happened? Try screaming and running in terror.