My favourite is called Genetic Memory: Many classic horror icons, such as Giger’s Xenomorphs, Silent Hill’s Pyramid Head, and other disturbing creatures, share common characteristics. Pale skin, dark, sunken eyes, elongated faces, sharp teeth, and the like. These images inspire horror and revulsion in many, and with good reason. The characteristics shared by these faces are imprinted in the human mind.
Many things frighten humans instinctively. The fear is natural, and does not need to be reinforced in order to terrify. The fears are species-wide, stemming from dark times in the past when lightning could mean the burning of your tree home, thunder could be the approaching gallops of a stampede, predators could hide in darkness, and heights could make poor footing lethal.
The question you have to ask yourself is this:
What happened, deep in the hidden eras before history began, that could effect the entire human race so evenly as to give the entire species a deep, instinctual, and lasting fear of pale beings with dark, sunken eyes, razor sharp teeth, and elongated faces?
… Just be careful out there.