How we change what others think, feel, believe and do
The classic horror story creates negative anticipatory emotion such as fear and terror.
A classic horror sequence is as follows:
The horrible event can include death of the person or a loved one, pain or transformation into a terrible form, such as one which inflicts in turn the horror on others.
Horror works slowly but inevitably, as in a dream where a dread threat creeps up on us but we are unable to resist.
In many classic horror stories, the source of horror comes from some supernatural source. This makes it both uncertain and unstoppable, both factors that increase terror.
Horror typically plays also on the natural fear or harm and death with which we are all programmed.
The best horror stories actually show very little monsters, blood, gore and so on. They create fear through the imagination -- which is much more effective at scaring people.
There is thus a different between horror stories and stories of horrible things.