With a little persuasion, any familiar thing can turn abnormal in the mind. Here's a thought experiment. Consider this brutal bit of magic. A human grows a second human in a space inside her belly; she grows a second heart and a second brain, second eyes and second limbs, a complete set of second body parts as if for use as spares, and then, after almost a year, she expels that second screaming being out of her belly and into the world, alive. Bizarre, isn't it?