Why, according to the narrator of James and the Giant Peach, are many people afraid of being alone in the moonlight?

The exact quote from the book is:

Most people-- and especially small children -- are often quite scared of being out of doors alone in the moonlight. Everything is so deadly quiet, and the shadows are so long and black, and they keep turning into strange shapes that seem to move as you look at them, and the slightest snap of a twig makes you jump.

It's in the start of Chapter 9.