How does Neil Gaiman use imagery in The Graveyard Book?

Imagery:

"There was a hand in the darkness, and it held a knife."
Chap. 1, How Nobody Came to the Graveyard, p. 2

"He reached in, and took out a card, only slightly larger than a business card. It was black-edged. There was no name or address printed on it, though. Only one word, handwritten in the center in an ink that had faded to brown: Jack."
Chap. 4, The Witch's Headstone, p. 127