 The entity is often amorphous. It's hard to see what it is exactly. It's kind of like often a dark black or dark gray figure without a face. In the Middle Ages, people described this as incubi and succubi. These were demons coming in to their bedrooms at night to harass them. In the modern age, it's, you know, aliens. Aliens are demons. And, of course, it's all in the minds of the people experiencing it. But for them...