All demons are products of humanity; all versions of Hell are built on the belief that Hell exists. Whether we generate this sort of monster without knowing it, or the demons choose to mould themselves around our expectations, or they simply exist in a way we can only understand by descending into madness on the level of Bosch... this is open to debate. What we can say with some certainty is that, Silurians notwithstanding, we have no race-memory of primal evil. True demons are demons because of the things we are, not because we carry a genetic Original Sin that reminds us of a genetic Origin Story. True demons are shaped by our ideas, and our ideas are shaped by the words we use to describe them.
"Except," says the Doctor - probably while fiddling with wires, and speaking ultra-urgently to make it seem as if this exposition scene has some sort of dramatic impetus - "that people get words wrong."
Or at least, their meanings change. "Nightmare" has nothing to do with horses. The "mare" part comes from Ye Olde Pre-English "merren", to crush: a nightmare is an invisible terror that shifts its weight onto your helpless torso, forcing the air from your lungs and pinning down your spirit. Fuseli knew this, and his painting "The Nightmare" (if you think you haven't seen it, then believe me when I say that you have, even if you don't know the artist's name) gives us a hobgoblin of All Human Horrors crouching on the chest of its sleeping victim. But as a visual pun, Fuseli chose to include the head of a monstrous she-horse at the end of the bed, peering through the curtains of the four-poster. Night-mare. It was meant to be a joke, and yet in the years since, it's been routinely assumed that bad dreams have always had hooves.
And if nightmares can be palpable, as they can in a universe of Chronovores and Weeping Angels, then they do have hooves: these days, that's what we expect of them. Still... of these Semanticores, these monsters twisted out of shape by language, the worst aren't the nightmares. Nightmares are at least allowed a certain dignity.
"Pandemonium". Increasingly spelt "pandamonium", but originally "pandaemonium". Pan-daemon-ium: all demons are here. Milton's name for Hell's Metropolis.
It wasn't supposed to have anything to do with pandas.
But here they come, out of the abyss of the misspelt mass-mind. Eyes as black as the pit, blunt teeth that chew bone oh-so-slowly, almost as if it were bamboo. Why the big paws...? So they can rip out your soul. Imagine that rage, the schizophrenia of being pitied (pitied...!) for your inescapable doom while being mocked (mocked...!) for your failure. The horror of imagined impotence. In all of our dreams, nothing else has become such a symbol of despair. So loved and given so much contempt. A golem of hatred and muscle that was only ever treated as a punchline.
As an animal, near-extinct. As a demon, a living, shambling scream.
Now is the age of the on-line. Language evolves, faster than ever, and so do all Semanticores. Combine this with humanity's increasing sense of wrongness, a guilt-fear that injustice has been done to All God's Creatures, but an equally-balanced guilt-fear of doing anything about it. The result is inevitable.
Prepare for pandageddon.
Of course, it should be remembered that I liked "Love & Monsters" but find werewolves entirely silly.