Lauren Destefano said this quote

There’s this anomaly that happens sometimes with twins. It occurs in the womb when the fetuses are growing too closely to each other. The stronger twin develops normally, while the weaker twin crumples and is encased by the body of the stronger twin, where it becomes a parasite. The result is a single child, plagued by a twin-shaped fossil inside. Like a tumor.In death Rose became Linden’s parasitic twin. They were two separate organisms once, growing steadily beside each other. Two pulses. Two brains. But she has crumpled and died, and still he carries her inside himself. She goes where he goes, feeling nothing, seeing nothing, a shadow behind his ribs.