Once upon a time, you went to an animal shelter to pick out a pet. You wanted a dog, but by some chance, you picked out a white dove and a black and red snake. You named the dove Aziraphale and the snake Crowley. Sometimes you suspect that these are not just pets. Sometimes you hear them speak human language, but you think you are imagining it. Sometimes you think that the snake is actually a demon and the bird is an angel. Now your pets are in the same room with you.