How long did it take for a past to die? - Richard Matheson

It was a fairy tale, no fooling. It was unreality becoming real. This frightened her. Because people don't care for unreality becoming real. It pricks their well-fed minds, you see, with something like a hunger pang. They prefer the logical stuffiness of expectancy. It is only at certain times that they weaken, letting imagination in. That's the time to get them. (“The Disinheritors”)

What would a Mohammedan vampire do if faced with a cross? The

The cross. He held one in his hand, gold and shiny in the morning sun. This, too, drove the vampires away.
Why? Was there a logical answer, something he could accept without slipping on banana skins of mysticism?