Creepifying the ordinary

There's nothing creepy about pinning living things to a board!
Nothing at all...

One of the most fun things about being a writer is throwing something unexpected into the fire.  Not the literal fire, no (unless you're writing campfire or mystery stories, then sure), but twisting something into a new light.

Nalini Singh, for example, takes butterfly collecting to the creepy by making it angels who get collected. One of her characters is known for his lovely blue wings, and he's had to continuously avoid being hunted by the archangel Lijuan who wants to pin him to a wall in her Guild Hunter series, a wall described in the second book of the series, Angel's Kiss.

The character, by the way, has been established with butterfly references since book one.

It's a case of taking something innocent and turning it creepy: Butterflies become creatures of nightmare.

Another example is Doctor Who's Weeping Angels. Graveyard statues come to life with a hint of evil. Did I say hint? These are some of the most terrifying villains in the series for me, although their method of killing is somewhat humane for Doctor Who [at least in the first episode of appearance]. Part of their terror comes from the ubiquity: who's going to look askance at a statue? Any given city, they fit right in.

Think about something perfectly mundane in your manuscript that appears in the scene whose tone you want to be dark. To create sense of creepiness, you can describe it with dark words: "The blade of sunlight through the window betrayed the mouse. A dart of fur as the cat sprang her trap turned into the mortal squeal, and then, there was silence." You can also set it up with foreshadowing, innocent references throughout that have a sinister cumulative effect:

"Hiya, Pip-squeak," her brother hailed her...
Her mousy brown hair kept falling into her eyes...
Nibbling on the cheese, she shook her head and scanned the cupboard. "I can't put out mousetraps. I always feel sorry for the poor things."

When the mouse dies, all those innocent references earlier suddenly become sinister, a hinting that fate is out for your protagonist.

Misplaced mundanity is another factor of dissonance. Taking something completely ordinary and putting it where it just doesn't belong gets it under the reader's skin. In some settings it can come across as absurd, when it borders on the line of fantasy... but placing it with something dark, or adding it to a dark scene, makes it eerie.

Walking through the shop, admiring the jewelry boxes cut in intricate detail, she paused at a grey, rectangular box. Was that? Yes, there was a mouse in the cold stone, head jerked back at an unnatural angle from its limp body. How lovely. All tucked away in its own little coffin... "Your cat, sir, seems to have brought you a present."

The shop owner didn't bother looking up as he tallied his day's earnings. "I ain't got no cat. Can't stand the mangy things."

Creepified by virtue of being a monkey.
It's watching you....

People, of course, are made terrifying by this last one: by being where they shouldn't be, by doing things that most people just don't do: the old lady at the corner store, who always wears a red ribbon around her neck, and smiles only at small children, the man who is seen too often hovering around the ladies' room, the same kid who shows up every place your protagonist goes, the polished gentleman who licks his lips anytime someone bleeds, the bonnie lass whose eyes light up and watch closely anytime people get hurt. The subtle quirks of body language are things we're attuned to by nature, and playing off those--using bits that just don't fit normal conversation--those are the bread and butter of the creep-factor.

How can you build the creep factor in your story? What are you trying to make terrifying, and how will you emphasize how eerie it is?

How have your favorite authors or directors successfully made something ordinary into something horrifying? What are some of the best examples of mundanity turned terrifying, and how were they achieved?