Is there something breathing under the bed? Check the closet. The monster category is possibly the oldest and most original horror genre of them all. In essence every horror film is a monster film. Typically the monster is a big, harry, drooling, creature with razor sharp teeth and nine inch long claws. But this is not always so. A monster can be as esoteric as a biological plague, as elusive as a phantom spirit, or as twisted as a human serial killer. Good monster films don't hold anything back and leave you with a slightly sick feeling at the end.