I never found this one scary..
The grudge loft scene made me jump.
Jaws got me when I was a boy.
And V made me terrified when little. (When they ate the mouse).
There was this 'hairy hand' flick which scared me senseless. (the hole in the dark bedroom wall was bound to have a hairy arm in it)
No other movie ever frightened me, I still watch every horror though.. Was never that keen on these exorcist ones.
I assume its scary to others, because it happens. How the hell they know that without knowing it, is beyond me.. Sort of.