Based on the search results, it is not clear what hunts inside the shadows. The search results mainly show a book titled "What Hunts Inside the Shadows" by Harper L. Woods and Adelaide Forrest, which is part of the "Of Flesh & Bone" series. The book is a romantic, suspenseful, and exciting story that takes place in a world where love collides with fate, and darkness conceals more than one can imagine. The story is about Estrella and Caelum, and it continues right where book one ended. The book is not a standalone, and it is part of a series. The search results also show a Reddit post where someone is confused about a nickname in the book, and a Goodreads page with quotes from the book. However, there is no information in the search results that answers the question of what hunts inside the shadows.