What kind of scenes in a horror film scares you the most?

When a ghost appears totally unexpectedly?

When the main character does not see the ghost sneaking up behind him?

When at the very end you find out the main character was actually a ghost all along?

But none of this compares to the feeling of arriving home alone and suddenly being stuck by a feeling of deja vu that you are reenacting the very same scenes in the horror movie you just saw! .. coming soon.